Glad to hear your vet is willing to take a look. Please let us know what you find out.
A side note, even though a lot of people do use DE as a "preventative" measure against external parasites, if you have an active infestation it is better to treat the chickens and coop with a Permethrin...
X2 I agree with @Eggcessive If vet care is an option, that is the best route to take.
He does have SLM, but I would be concerned about the wounds getting/being infected. The photo does not completely show his feet, but they look to be inflamed as well(?)
Not to scare you, but a while back...