I don't see why not, I've seen several pictures of rear exit exhausts on this site.
I don't see much advantage to it, however. There is the small risk of plugging up when backing into deep snow, and I saw on one site (Gibson's, I believe) that they don't recommend that you tow a trailer with a rear exhaust (due to fumes - maybe a bit of a stretch?).
Anyway, I went with a side-swept when I upgraded, but if you like the look of the straight pipes and don't find either of the factors above particularly troubling, go for it.
