Hi Gary,
I always use one reverb for the entire mix. Exceptions are sometimes with vocal libraries that contain their own reverb and software synths that also might have reverb. In this case I used a vocal library made for Kontakt and may have used it's own native reverb but I really don't remember as it was a number of years ago. In general though I find that to create a cohesive space, using fewer reverbs is better than using more.
Jerry