Well I guess he shouldn't have said that Red Bull is poison, considering that nutritionally pretty much all energy drinks are the same. But I guess Rockstar didn't mind too much, they signed him, and I'm sure both parties are more than happy with this arrangement.
I wouldn't think twice about letting an energy drink company pay me money, even though I know it's liquid poison. I probably wouldn't go around saying that it's poison though, might be a bad business move.