first off if you ask any real coach if tramp translates to snow they will tell you not at all excluding simple flips (backies, fronts, flats, etc) the pop is different the throw angle is off its not at all the same. if you go to any ski training facility all the little kids can throw dubs, but can they cork 7 or rodeo 5 on snow, nope. the only thing trams really train is air awareness, which is essential.
a summer rail setup translates immediately to snow, so if you want to get good at rails fast and have a nice big backyard than the setup is easily the way to go.
i think tramps are way more fun though