Far as I know, and in my experience, the bats won't be near enough to the people or the bunnies for a tick to crawl from them onto anyone. They're nocturnal and very shy - the little bat we took the picture of was a very very rare occurance, and Paul was several feet from him when he took the picture. Mosquitos are far more annoying, are known disease carriers, and will attack any warm-blooded creature.

I found the following information several places on the web:
Bats may carry parasites such as mites, fleas, or ticks. Fortunately most bat parasites are host specific, which
means they rarely bite pets or humans. After bats have left their roosts, any parasites that may remain quickly die.

Bats have a much worse reputation than they deserve, but then again, so do whatever breeds of animals Hollywood has decided to cast as "villians."