Well its possible to give you ideas maybe be a bit creative in your dreams but actually getting lyrics or solid ideas in a dream would probably not be completely possible, your more likely to think of something in a dream, play it when you wake up maybe on an instrument or what not and then realise that it sounds just like a song you've heard by another artist. You may find a bit of copying going on in your dreams if you try, its just a theory though, it may work, try it out though and prove me wrong, cool idea though.