If his enthusiasm translates into major stage charisma, it just... might.... work. Especially if the crowd has been drinking a lot and he can rev them up.
Otherwise - tell him like it is. He's got to either get on pitch and hit correct notes, or the band needs to find a singer who can. Audiences really do notice a crappy vocal much sooner than they'll notice a crappy bass line.
Otherwise - tell him like it is. He's got to either get on pitch and hit correct notes, or the band needs to find a singer who can. Audiences really do notice a crappy vocal much sooner than they'll notice a crappy bass line.