Yes - 7 dust works & they don't get sick or seem to have any other problems with it.
You don't want to over do it though.
I saw a post here a few months ago where a guy moved an old board & found tons of bugs. He covered them with 7 just before his chickens found the bugs and ate them, 7 and all. He said he was sure the chickens would be dead in the morning, but miraculously there were no side effects. Chickens were fine.
I've used it several times myself as a preventative & had no problems.
My chickens get to take a fluff bath in cedar saw dust. Even the silkies love it. Haven't seen any mites or bugs & I also dust the chicken house w/diatomecious(sp) earth then put regular shavings in it. I think Sevin says you can dust your farm animals w/it. Just not the chicks (or be careful). Check the wrapper.
You can mix Sevin with food-drade DE, and also use the DE in bedding, nest boxes, coop porches and on the earth in your runs.
Another way to keep pests out of the coop is to hang no-pest strips made by companies like Black Flag, Vapona, Home Hardware and TSC high in the coop away from birds and their food/water. The pyrethins keep out ticks, mitesl fleas, flies, mosquitoes and gnats.
This information helped me decide to use a poultry dust containing Permethrin instead. We're also using food grade DE in several ways (dusting them, in their food, and in their bedding & nesting boxes), and giving the chickens a dusting area with it, which they love.
Food Grade DE is just that, safe to consume by humans. To be food grade it must have less than 3% crystalline silica content, the harmful stuff in non-food grade. Non-food grade DE is lethal! For answers to any questions you may have see www.freshwaterorganics.com/what_is_de.htm