Every time I've used wood in my tanks, I've gotten mould growing... never orange mould though, just white mould. I'm pretty sure white mould is harmless, but I'd get rid of the orange mould- bright colours in nature tend to be a warning- "Don't Eat Me!"

I always get rid of mould, but that's just personal preference because I'm a clean freak. It shouldn't bother the frogs, but as I said, its down to personal preference. Whenever you have plant or organic matter in a moist environment, you'll get micro-organisms growing. Boiling logs will kill initial organisms, but won't prevent new ones from growing and breeding.