Being a veggie won't be too much of a hinderance. Veggies MREs are more than plentiful since they ****.
As for OCS, you are not allowed any sort of supplements or pills while in training. The only saving grace I could tell you is that if you go traditional, you have 28 days to stock up on protein pills in your system before your weekend OCS drills. You'll only have to deal with 2 days of no popping. If you go Fed OCS, well. Good Luck.
"Fate protects fools, little children and ships named Enterprise"