Yes, but the stall will occur first and provided you recover from the stall the spin will not develop.
In a perfect aeroplane with perfect rigging, flown perfectly in balance with no propellor effects, both wings will stall at the same time and a wing would not drop.
As these conditions will not exist, if you want the aircraft to stall both wings at the same time, I would suggest that the rudder is used to prevent or induce a yaw to try to cause each wing to stall at the same time. To achieve this may well involve the balance ball not being centered but the result is each wing will stall at the same point due to all the variables being equal.
You are closer to a spin if you stall with wings level and a side slip than if you stall with a wing drop and no side slip.
Spin requires stall, departure (i.e. none or negative roll damping, i.e. uncontrollable roll) and yaw (e.g. side slip). If you set up a side slip before the stall in a misguided attempt at preventing a wing drop you are already one step closer to the spin, especially keeping in mind that a side slip will lead to the wing drop. The departure/wing drop also leads to a yaw eventually, but that yaw tends some time to build up.
By recovering from the stall after the wing drop but before the yaw builds up you will prevent the incipient spin from developing. Doing it the other way around, recovering after the yaw but before the wing drop, will not be likely to work.
In my admittedly limited experience, yawing/side slipping at the stall will always lead to a wing drop before the stall recovery, but a wing drop at the stall will not lead to significant yaw or an incipient spin. I know (as in have been told that) some planes will always produce a yaw after the wing drop before stall recovery is complete, but I do not believe there are many planes where a wing drop produces yaw but where a yaw does not produce a wing drop. Consequently, preventing the yaw is always the number one priority to avoid an incipient spin, whereas preventing a wing drop is the second priority.
For Pilot DAR's test flights, I don't suppose the testing criteria will be met if he stalls with wings level and a side slip...
As for why the wing drops: Preventing a wing drop does not necessarily require that both wings stall at exactly the same time! Some roll damping can still remain even if pitch stability is lost. This is because roll damping is primarily provided by the outboard parts of the wing, whereas pitch stability and vertical damping is provided by the entire wing. If the inner wings are sufficiently stalled for vertical damping to be lost (i.e. the aircraft settles straight ahead) or pitch stability to be lost (i.e. the nose drops) while the outer wings are sufficiently unstalled for roll damping to remain, the aircraft will not drop a wing. That is how modern aircraft are designed.
If preventing a wing drop was dependent on both wings stalling simultaneously, it would be a rare exception that an aircraft would stall without a wing drop. That is not how it works at all. It is the roll damping that prevents the wing drop.
In other words, maintaining aileron effectiveness during a stall is a secondary reason why we always want the inner wing to stall first. The primary reason is to maintain roll damping during the stall. Preventing a wing drop by having ailerons effective but no roll damping, thus relying on the pilot to balance the plane and actively prevent a wing drop, would be very hard and rarely successful. Preventing a wing drop by having remaining roll damping is automatic, the pilot doesn't have to do anything. Roll damping during a stall is the most important thing; aileron effectiveness is secondary.
And contrary to what a previous poster said, the airflow generated by the propeller has everything to do with why a wing can tend to drop at the stall; at least it is one of the most important factors. For example, the helical prop wash hits the two wings at slightly different angles of attack, tending to cause them to not stall at the same time near the roots. If sufficient roll damping remains, this will still not result in a wing drop, but if there is insufficient roll damping then this assymetrical slip stream effect is one of the reasons why a wing will drop.
On the relation between roll damping and use of aileron: Roll damping is what stops a roll if it develops; aileron control is used a return the wings to level after the roll damping has damped out any roll disturbance. If roll damping is so low that the pilot actually has to balance the wings using continous aileron input, the pilot will most likely not succeed for very long and this will cause a wing drop. If the pilot tries to achieve the same thing with rudder, the risk of over controlling is much greater (since the rolling moment is a secondary effect to rudder input, after a yaw has already built up), and the result if one fails are much more dramatic.
Again: Attempting but failing to keep the wings level with rudder results in all three pro-spin factors to be present; stall, yaw and roll. Attempting but failing to keep the wings level with aileron only results in two factors to be present: stall and roll. In the latter case, recovery can be made before the yaw builds up.
Edit: Forgot to point out that when I mention "aileron input" I of course mean coordinated aileron input! As always (except possibly in cruise in some aircraft...) when the aileron moves the rudder should move as well. But this rudder movement is not intended to cause a yaw but to prevent a yaw. Getting that wrong and using only uncoordinated aileron will of course cause a yaw and a side slip and that will mess up everything. But this coordinated use of rudder to prevent the adverse yaw due to the aileron input is completely different from the uncoordinated use of rudder to cause a side slip with a secondary rolling moment.