where would you get dispel that early in the game? and sacrificing a wisp to kill a wolf at such a crucial point in the game is just suicide, and that's only NE. and i doubt anyone would make a shop just to get a dispulsion wand (i'm actually not sure if any of the stores have it).
i've never tried SH rush with serpents, but i'd guess it'd be pretty useless. level 1 serpents are crap no matter how you look at it and are good only to make worker units panic. however, coupled with a grunt or two would probably triple your rush strength. still, i've never seen it ingame so i really wouldnt know.