I'm definitely raising because when someone is putting in that much money that often with nothing, you want to be able to take it sometimes even when you have a hand that won't win at showdown.
Why not just wait until the turn to do this? Seems like we get more information that way. Not to mention it allows us to see free rivers if we feel like it and allows him to make bigger mistakes on later streets (which he isn't good at playing). And we get to raise the turn all in if we have a good hand which is a nice weapon.

I suppose he might call down with weak value that he wouldn't if you raised flop...or would he? I'd imagine someone who is cbetting every flop is going to be forced into calling quite a few raises.