If i was Fury i would jump at the chance as he really needs better sparring imo, it would help him out a lot.
Unless he acts like a twat and tries to knock Haye out in sparring i could actually image Fury trying to do somtheing like that lol.
that would be decent prep for haye. Fury has to be careful though, he was caught with loads of overhand right by mcdermott and that right hand is hayes best punch and will be the most useful against the beast from the east. If it gets heated i can imagine the hayemaker knocking fury down a few times.