There is no prohibition on non-personal use, and there never will be, since that would mean Prime account holders wouldn't be allowed to use Prime shipping to send gifts to other people, for example for Christmas.
There are two relevant prohibitions in the US amazon terms:
> Prime members are not permitted to purchase products for the purpose of resale, rental, or to ship to their customers or potential customers using Prime benefits.
He's not reselling or renting the food, so this isn't an issue.
> You may not transfer or assign your Prime membership or any Prime benefits, including promotion codes for Prime memberships or benefits, except as allowed in these terms.
I don't know what his tax structure is, but this is potentially relevant. The simplest possibility is that he receives money in his personal capacity as a sole proprietorship, spends it on food, and deducts the whole amount as a charitable donation. (I have no knowledge whatever of the Canadian tax system, and really only a little of the US tax system.) Assuming that works, he's fine. If that doesn't work, he'll either need to incorporate the charity he's running or pay taxes on the donations he receives. Letting other people directly pay for his orders, such that the money doesn't flow through him, would violate the non-assignability of Prime benefits. If he incorporates as a charity, the charity will need its own Amazon account; it can't use his.
Amazon does offer business accounts with two-day Prime shipping, but their pricing appears to be purposefully unadvertised.