Food grade DE will not work for leg mites...but it's not bad to have around for other mites....
I rescued one chicken that had leg mites so bad that her scales were falling off....lets just say that the typical vaseline, olive oil, vicks, etc treatments were not enough. They would seem to start working and then get worse again. I think the "infection" was so deep, the oils did not reach the deep ones. Those treatments work if you catch it early, but not for advanced cases. I don't typically use medications, but in this case I had exhausted all my alternatives... Pour on Ivermectin...3drops on the back. It's not labeled for chicken use, but it works and many use it this way. Some people say you don't even have to have a waiting period for eating the eggs, because there's no waiting period for when they use it on cows and taking their milk.....but, I waitede 7 days for peace of mind. (oops, I just read it was a rooster!.....) oh, I would vaseline the legs of all the chickens, do it 7days apart *2 treatments.....if the roo has leg mites...it's likely your other hens have a mild case as well.
By the way, that chicken I rescued.... I was told she was too old to lay eggs....but she had all three types of mites, and she is now one of my best layers and has XXL sized eggs. I swear she's saying THANK YOU with every egg!!!
Good Luck-
Sandra