I don't know how many polies that Orion Scout has bc I haven't DL yet but if it's high or standard for a ship that size; I wouldn't recommend using it as a fighter bc there's never just one, there's always multiple fighters therefore you'll have a slight lag depending on your system's specs. If it's low then it's okay. Just something to think about.
Fighters and shuttles usually have small textures and low polies since you can barely see them up close.
I believe the limitation is not the model polycount itself but the ability of the game engine to handle the number of ships/fighters in game.
Ten years ago, I remember playing a game where there was so much on screen that it frame skipped until ships were destroyed and there was less to render. I doubt my current PC would have this problem.
The base models DD has historically extracted from other Trek games don't tend to be all that big. I was just looking at this as an experiment and he'd be in the best position to advise.