My Varanus isn't capable of using the skin either; I think it's only for Klingon ships. The only reason I'm not complaining is that I'd never see it anyway, since my Varanus is a purple polaron people eater. I can't apply it to the Galor on the Fed side, either, but this also doesn't bother me, since I want it to look like a Galor.
So, from what I can tell, it only works on Federation and Klingon ships; no Gorn, Orion, Nausicaan, Catian, Cardassian, Vulcan, Ferengi, or Jem Hadar vessels. I'd at least like it to be applied to the ships that come from the member races of each faction, though, even if lockbox ships are excluded; considering that the skins seem to have been carefully patterned on each ship differently, I imagine this takes time, and is most likely already underway. Just a guess, but...I think we'll see it in the somewhat-near future.