There is water available.

Yes, the dump station has a potable water supply to use for filling your RV tank.

There is also potable water at the dump station (and I assume some spigots scattered throughout the campground). Apgar just down the road also has a dump station with potable water and multiple fresh water spigots in every loop.

I do not recall. However looking at this map, it indicates that there are water spigots located around the campground. https://www.nps.gov/applications/glac/images/fish.jpg