Well, first off, you'd probably want to use the Nurgle guys as the main, and the DE as the allies, as that way you get the superior objective holders able to hold objectives. Also, unless Nurgle is your Primary, you can't have Plague Marines as a troop choice.
You seem confused about your fliers. Heldrakes aren't all that when it comes to anti-tank; the Voidraven is. The Heldrake is outright lethal against infantry though.
I think to make this work the footsloggers need some serious ranged presence. Elsewise it will be very easy for an opponent to ignore them for a couple of turns while shooting down your fragile Dark Eldar. Also, if you're running splinter spam and a Heldrake, your anti-inf needs are fairly few. Killing tanks however looks far more of a priority for the rest of the army.