Short version: no.
There are two types of paintball cylinders: Co2 and High Pressure Air (HPA) / compressed air tanks. The Co2 tanks are a definite no; they aren't rated to contain the pressure from compressed air, and obviously using them filled with Co2 is counter-productive. Paintball facilities that fill HPA tanks do filter their air to some extend, but definitely not enough to be considered safe for SCUBA use. If it's not rated for a breathing application, I wouldn't put it in your beer.
I've worked and have been involved in the paintball industry for 12 years. I've seen how most field compressors are treated maintenance wise. I wouldn't consider doing it under any circumstance, unless you bought a BRAND NEW cylinder AND only fill it at a dive shop with superbly clean air.
Joe
