Raonic questionable on grass. He has not shown much ability on grass. The serve of course very beneficial, but lack of experience and poor movement hurt him much more than the serve helps him, even if this is grass. I won't entire count him out though. Isner similarly is someone I would question. Sure, he did good in Newport, but the pressure won't compare to Olympics/Wimbledon especially against the best in the world.
Roddick is one to watch out for I think. The British crowd always cheer for him, he has found some form again, his confidence should be high enough, and this is best of 3 which works perfectly because he still needs more time to be ready for best of 5 matches IMO. In fact, if Roddick wins which is either way quite doubtful, it would so great. At least he wins at Wimbledon in some way