I have wanted to try it, I have a pink toed tarantula and many orchids...my spider requires high humidity and live plants. His substrate is very close to orchid requirements and I seriously wonder if I replanted one in there if it will all work out. My spider eats bugs and spins webs, nothing that will hurt an orchid.
Not heard of this, but I've heard of lizards & frogs being kept in with orchids. I think that's what our site owner Marty has done in the past and there have been others over the years talking about it as well. (Marty's other forums are on frogs and vivariums).
I can't see why it wouldn't work if the requirements are similar.