I've given a few of my chickens louse baths, with dog flea shampoo, to get rid of their lice. However, I really wouldn't recommend it. It's really toxic stuff, and even made me feel a bit queasy, so I only used it once. It got rid of their lice, but I'm not going to do it again.
There is one very good natural solution we've tried: tea tree oil. All you do is put about 1 tablespoon into the bath water, making sure not to get it into their eyes. I use it on dogs too and it kills fleas like nothing I've ever seen. The only problem is that it can cause dermatitis if too much is exposed to the skin, thus, the diluting in water.
I'd rather my chickens have lice than compromise their health. Usually, they just go around taking their dust baths, and that's enough.