Roger,
Well bees can hear... they do so by sensing vibrations via an organ in their hind legs. Of course their hearing isn't quite the same as ours. But I'd call it hearing none the less.
Anyway, to answer your questions, I had the same fears when I was starting out, but found that the bees really don't pay any attention to the lawn mower, even when the exhaust was pointed right at the hive entrance. I mow right up to about 6" from the front of the hive and they don't pay any attention to it... the last 6" is part of a flower-bed that doesn't get mowed but does need weeding from time to time, but I just hand-pull them, the bees don't pay any attention to that either.
But here are some tips for mowing that I think helped me...
1. If you have a walk-behind mower/push mower stand to the side of the hive and push it in front of the hive, that way you're not standing directly in the bees' flight path.
2. Mow in front of the hives in the morning or evening either before the bees become really active for the day or as they are winding down for the night.
3. Wear a beesuit? Ok, I know this is the wuss thing to do, but the first time I mowed my lawn after getting bees I was fully suited up, and after doing so I realized that the bees weren't even trying to get me and doing that gave me the confidence to go without the beesuit.