Yeah, I used to put clones started in rockwool directly in soil. Works great. I also used to mix the old rockwool cubes in my soil, just to get rid of them.
I wouldn't. Mine eventually started to turn green after the transplant to soil. If you sterilized them first, baking them in the oven or something, seriously, they should be fine.
yes you can put rockwool into soil. i use rockwool for making clones its easyer to get air into the roots with rockwool when the babies are ready i plant them in soil. Peace