Oh I assume yes the dual wield perks will work. I highly highly doubt the power attacks will work with daggers. Dagger decapitate? don't think so
Well, I'm going to try getting them anyway. I intend to get every perk in one-handed except for the ones that specify axes, maces and swords. Once I get the game, if the description for the perks or the strategy guide mentions that those other perks aren't applicable to daggers, then I guess I'll have to change my build, but we'll see.