It depends. Do you want the vocals and the keyboards to have the same reverb on them? If so, then bus them to the same reverb. There is right or wrong answer. It boils down to getting the sound you want.

If it feels good, do it.

I always bus my vocal effects to their own dedicated effects and often have separate and different effects for lead vocal vs backup vocals. Synth's, keys, drums, guitar all get their own dedicated effects as well.