This is probably old news, and I'm sorry if it is, but if you do his daedric quest after completing the Dragonborn DLC, he has some new things to say. Unfortunately, it's only a line or two. The DLC also causes him to show up in tentacle form there instead of the black void that he used to be. So I'm curious, if you do the DLC and have already done that quest, agreeing to be his champion, does it have much of an impact or is it also just a tweaked line or two?

He recognises you as his champion, thats about it.