Actually, with a good bit of F&B finance experience the first part of the logic holds up - namely Brad was tipped for the service of pouring the beer and therefore it is his money and he is free to do with it what he pleases.
A few assumptions here though:
1) no signage or inference exists to suggest that the tip is going to the charity or the club.
2) If it appears the transaction is a single transaction this gets dicey - If Brad brought his tips home after divvying up the jar with me and then decided to donate, fine, but if we just handed over the jars, not so much
3) Brad claimed it as income on his personal taxes as appropriate (oops)
4) I probably would not want to even think about it if Brad was serving his own beer though - even more dicey