It might be better just to focus upon less scheme-marker dependant schemes when you have them, such as Distract, Cursed Object, or even Assassination, Murder Protege, or Bodyguard. That would allow you to stay together in a little death cloud near Nicodem.
It's not a perfect solution, but something to keep in mind.
Note that poison triggers at the end of the turn, not during a model's activation.
I've found that with summoners, you're generally better off using your soulstones to add suits to high cards in your hand, rather than trying for the on your casting flip. The odds of lucking into a high crow are rather low.
Punk Zombies and Iron Zombies are pretty decent, and as others have noted, Belles are also pretty good. The Hanged can also be very good for neutering Masters and Henchman, so I would put them on the list of models to try out.
I've found that decay is best used to both damage enemies and to heal your own models. Remember that you can target your own models and cheat in a low card on their defense to get the Blasts in the middle of a melee.
Using Rigor Mortis to debuff the enemies while your undead take them out is also helpful.