I don't see anything about how many grad students might qualify for SNAP. Based on the requirements for SNAP I'd guess that it is a very low fraction.

According to the Massachusetts SNAP eligibility site, a grad student earning the minimum Harvard grad student salary would have to be in a household of 3 people with neither of the other 2 working to qualify for SNAP.

If your household has you and one other person working, and that other person is working half time earning Massachusetts minimum wage, you'd need to have 4 people in your household. The the other person who works is working full time you'd need to have 5 people in your household.

If both people working are Harvard grad students they would need 6 people in their household to qualify.