Experienced paint guys I have a question

Depends on what system (brand) they use, and what the manufacturer of the paint specifies. I remember about a year ago we were trying a Valspar waterborne system, dont remember the exact name, but you could spray that over any primer. Now we're using the Onyx system which tells you to use their brand of primer for their waterborne base.

Not sure what would happen if you didn't, I'd venture to guess that it would be fine as long as the usual preparation was done right, but if the painter doesn't use the primer the system specifies, most manufactures wont warranty the paint.
which is why its always better to use the same system all the way through (primer-base-clear)