Parson proved that you can take corpses into the magic kingdom. That gave me an idea for a possible somewhat morbid Erfworld industry: corpse trading.
Here's how it would work. Sides without a croakamancer, who have no use for corpses, would bring them to their portal and push them through.
Free croakamcers in MK would collect the corpses and take them through the portals of sides that hired them, to supplement their army with uncroaked units.
The croakamancer would animate the bodies, collect their payment, and return to MK. Then they'd visit the portal that provided the bodies to give them a share of the money.
It might not be worth the effort for weaker units, or uncroaked that are poorly animated, but if your side kills something like a warlord, and a master croakamncer can restore it to near living power for several turns, that could be worth a lot of money if you found the right buyer.