If you take someone's name for your restaurant then I think you should at least acknowledge said person. Unless it is a coincidence and there is another person named Tim Horton that the restaurant is named for then there should not be a problem. It all depends on how the owners of said restaurants feel.
Tim Horton donut shops should absolutely honor his legacy and his contribution to the chain that bears his name. He was co-founder of the donut shop in 1967 with Ronald Joyce. He only lost his part of the business due to a tragic car accident and for that reason alone should be recognized by the franchise.
The donut shops that bear the name Tim Horton have many opportunities to honor this legend. I don't think that they should be required to honor him, but they have a great place to do so. They are benefiting from his name as fans stop in for coffee and donuts, so he deserves to be honored by the company.
Yes, Tim Horton should be honored by the donut shops that he founded. Some small acknowledgement would be satisfactory in this case. For example, they could name a donut after him or have a special offer on his birthday. I think it would be a nice gesture on the part of the shops to honor him.