Does Lovecraft himself appear in the game, in any way?

Avi made a custom herald meant to be him and I've seen a custom investigator floating around somewhere, other than that I don't think so.

http://i622.photobucket.com/albums/tt307/avi_dreader/TheArbiterofReality.jpg

Thats really cool, may have to make one when I start playig the game, at least to have him somewhere on the board watching the horror that unfolds with each game

Hail Cthulhu

Well...there's Earl Sawyer: http://www.arkhamhorrorwiki.com/Earl_Sawyer

Striking resemblance.

At least now we know what H.P. Lovecraft would look like if he were drunk or stoned

Randolph Carter would make a great investigator - and a story for him (pass/fail) could be that he gets the Silver Key card and brings it to another Dimension.

There's a mythos card that's probably a reference to him.

Randolph Carter was probably an alter ego of sorts for Lovecraft; he's about as close as I've seen to actually having Lovecraft in the game.