Sure you can set both RMI needles of each RMI (LH and RH) to one ADF, if there is only one ADF installed in the aircraft and both RMI's are connected to that ADF, which is the case in our aircraft!
The slight problem some folks have, HOCHWALDSPRUDEL, is that...because they have never seen a particular avionics arrangement, they therefore apparently make up their minds that it could not possibly exist.
I would call this....closed minds.
And yes, there must be a resolver in any ADF system, as otherwise manual direction finding would need to be used...and yes, I've done that, too....long ago.
Going further, some folks think that an ADF cannot be used for reasonably accurate navigation.
They would be quite wrong, of course...perhaps because they have not been taught properly about NDB navigation in the first place.