Lee Marvin in anything was a good thing but it's unlikely that a movie star of his magnitude would have appeared in a t v show like Star Trek. His last tv appearance was in 1965, on Theatre of Stars (he'd one quite a bit of tv before then). But the same year, he won an Oscar for Cat Ballou, moving into major movie star status and it's highly unlikely that he'd have gone back to tv (remember what Christopher
said earlier about tv being looked down on by movie stars).
His movie Hell in the Pacific is the sort of story one can imagine forming the basis for a Trek story (the sci-fi movie Enemy Mine is heavily influenced by it).
It's easy to imagine Marvin turning up in a Star Trek movie in the 1980s. An alternative Captain Krug, perhaps?