I would say - treat the cut first - then do your treatment for scaly leg mites.
Depending on how bad the cut is, you may need to wrap it for a few days - I like to use gauze & vet wrap for foot wounds.
If you are able to catch him, you might find that wrapping a towel around his wings (with feet exposed) is helpful in "subduing" him enough to get his foot treated/wrapped. This is my method for anytime I need to look at/treat feet for any reason - if they cant flap, they struggle less!
Hope that helps!