I think that if you have a good or expressive drummer then they need to hear the other instruments just as much as other instrumentalist need to hear a beat. If you're playing with bam-bam the psycho animal then it probably doesn't matter. I not trying to be an ass (sorry) but I truly believe that a drummer with skill does best when they can hear. If the guy can't hear it's a problem. Again; why can't the guitar and bass players just angle the amps a little? Is it about looking cool? Big amps pointed straight out?? I've played with amps on the stage side pointing in (no one dancing could see them - didn't phase me if I could hear).