As a Franchise Attorney I can tell you the following. If a lawsuit for food poisoning is brought, you can be 100% certain the restaurant will be a named Defendant. This means having to defend, and that's not cheap. Of course, appropriate insurance may protect somewhat, but with the third party supplying the food, even that is uncertain. Consult with a good business or franchise attorney in your area for specific advice.
Mr. Franchise - Kevin B. Murphy, B.S., M.B.A., J.D.
Franchise Foundations, a Professional Corporation