Does anyone know what's the legal status of using formats such as .bsp (made by id software I believe) in a commercial game? I thought you could then leverage the various available tools for editing maps this way. p.s any other formats with available editors?

IT's not, you can use any format name as you like, but you should not use COPYRIGHTED content, like original .bsp files from cs 1.6 or smth like that ;)