Go to the USDA.FNS.GOV/SNAP. If your benefits from the GI bill is more than $1276/month, then you fail the gross income test. It's not that you are receiving money from the GI bill, it is probably because you are over the income limit. I checked the FNS website, I didn't find a GI bill exclusion.

This website has tables on eligibility and link to state websites. Good luck!