Since banks are regulated differently (OCC, FDIC, FED), is it possible a cannabis businesses will get different treatment from their banker depending on the bank's regulator?

Not treated differently but there may be some differing compliance and due diligence requirements imposed by individual regulators. The overall objective is to assure to the greatest reasonable extent that the beneficial owners of the MRB as well as all funds deposited are 'clean' and accounted for, and there is no co-mingling of funds from other enterprises, particularly illegal ones.

Of course, it would not be unheard of that an individual financial institution might use the pretext of who their regulating body is to deny service altogether.