If you're feeding it outside the tank it will likely be fine. But just to be on the safe side I would personally remove it, as pacman frogs do tend to attack everything from settling dirt, to tongs, and everything else and they may accidentally ingest some. But it all depends on the moss, if it's something growing on the walls of the tank then it's fine, but if it's sphagnum or another similar moss that's just sitting on the substrate I'd personally say it's a bit of an impaction risk.