From what I picked up during the invasion, I rather doubt that the monster/undead reinforcement rates were tied to the values that govern mundane undead and monster spawns. Unless those values are already linked behind the scenes to the factors that became evident during the invasion, which would be interesting...
The invading monsters ate people. They were like locusts. They'd move into a region, eat thousands of peasants overnight and have a shiny new army in the morning. The undead GM dropped hints that battle and death all over the continent contributed to his available reinforcements. Presumably this might have included peasants who died (of starvation for example... or of being eaten by monsters) in addition to soldiers. I never knew about the daimons, though I suppose their reinforcements came through portals to the netherworld or some such.
