Are there any foxes in the Redwall series who are good guys?

No.

Out of all the vermin species, I'd say the closest it had to a good guy was the rat who became a boatwright at the end.

You had one ferret (Veil) who sacrificed himself to save a friend, another (Romsca) dying from battle injuries to save an innocent. Maybe a few others with a twinge of conscience. But out of the foxes, they were just nuisances in general in the first Redwall, and considered vermin in the others.