I think Agaricus has some very valid points.
You *can* use V/S and speedbrake together but over the years I've observed that it requires more attention than other ways of getting the same result. Wind gradient, icing, config. and speed changes all need continuous adjustments in the amount of speedbrake.
If you're distracted by other duties or events, which normally happens during the approach phase when speedbrakes are needed, you can easily end up with power coming up against the spoilers or getting close to limiting speeds, especially with a significant V/S or flap deployed. Yes, if you're on top of it all, it can be managed without incident but, to me, it lacks... Elegance, or something close to that. I feel part of being professional is to try to leave as much spare capacity as possible to deal with unforeseen events (or even foreseen ones...), especially when in a busy environment.
All AFDSs that I know of prioritise V/S over anything else, so the speed will vary unless you keep a close eye on the instruments and move the lever around. In the terminal environment, ATC generally want you to fly constant speeds and vary the RoD, rather than the other way round. It's simpler just to use an open descent mode (level change in Boeings) and adjust your descent rate using more or less drag. This has the advantage that the aircraft is speed stable if you take your eye off the ball for a moment.
V/S is one of those modes that if used thoughtlessly or without due monitoring can put you in a situation you'd rather not be in, such as behind the drag curve at high altitude if you climb/descend into a decreasing headwind or increasing tailwind. Strong temperature gradients can produce unexpected results as engine power decreases along with mach number. Things like this occur because it is easy to set a V/S which is instantaneously OK but will sooner or later take the aircraft out of its performance and/or flight envelope.