To be honest, I have not yet come across it but it is very very possible -
Ich (white spot) is a disease that acts like an aquatic parasite - There is nothing that would make frogs be immune to the parasite.
here is a pretty good website regarding the treatment and prevention of Ich.
Cause, Treatment, and Prevention of Ich in Freshwater Fish
Also, read up on salt baths. In summary,
For daily salt baths, take a spare container (Tupperware or a Kritter Keeper) - add one gallon of dechlorinated water around 72* and 1/2 Teaspoon of Epsom Salt. Let the frog remain in here for an hour. The discard the water and return the frog to its tank.
Salt baths are a great way to help the frog fight off disease and infection - they are quite tolerant of them in comparison to fish and would help with the Ich infestation.
It would also help if while the frog is in the bath, you do the massive - (M.A.S.S.I.V.E) - cleaning out of its tank!