IME they do not harm the frogs. I just pull them if I see any. They don't seem to reproduce that fast so plucking them helps keep the population down. If it is a Millipede you should be fine, but a centipede could give you some problems.
Try the lettuce trick. I saw a few slugs in my tank a while back and wanted to see if it would work. I didnt get any slugs on the lettuce inside the vivs, but I did get 2 millipedes from my plant grow out tank.
Yep just throw in a strip of lettuce at the bottom of the tank, it will attract what you don't want in there. Take it out, tap it over the trash can, then place it back in the tank. Repeat until there are no more culprits!
I've had these in my regina tank for years. I will pull them when I find them mating, but will leave them when I see 1 or 2. I like having a few in my tank because they seem to do a good job as janitors, eating dead ff's and decaying plants.