a foxs teeth would make quite disctinct marks (vry similar to small dog, fair enough) ..this does seem very odd, because this kind of thing is extremely rare.
my first thought was a fox that did this might be in a very bad way, as generally this kind of odd behaviour is performed by animals suffering illness (such as the rats in our house chewing some odd non-food items after the poison went down).
i still favour a live and let live approach to foxes, i mean, its hardly a common occurrence, and foxes are everywhere.
feeding foxes - i wouldn't, but then i don't want to encourage them into our garden, as it would upset dog, and their mess carries worms. on the other hand, it probably makes buger al diffeence whtheryou choose to feed the or not - this time of year (BBQ season!) most people will be feeding them one way or another.
incidentally, lyme disease is caught by being bitten by a tick (generally found on deer or sheep) - not from dogs (though dogs can catch it, it killed one of ours ).