Saltwater bacteria will die off at about 1.008 concentration of specific gravity saline (I thought...), or about half of what is minimally required to be sustaining saltwater fish. So it will not survive or flourish in freshwater.
The ceramic media though, as well as any filter media like bio-ball are compatible though with freshwater, and freshwater nitrifying bacterias will colonize on them just as efficiently. One may use any of the available bacteria starter solution or traditional methods of having something decompose in the tank.
Most people will agree, I think, on NOT using fish or livestock to start the bacteria colony these days however... if an alternative is available for the sake of the fish not having to stress through it and possibly be a fish you won't want in there in the end for a specific community/compatibility.
A protein skimmer needs a high surface tension of saltwater to work. IN freshwater the bubbles will just combine and become so big that it will not create a foam and just end up making a watery mess in the nearby area.
At best, it will just waste a lot of electricity for doing only thing beneficial to the tank of helping gas exchange, which can be accomplished with less power with a wand and air pump.