@Nagumo I had thought about something similar years ago but I'm trying to establish if you're asking whether all the enemies are made like ID's? For every single enemy of Dracula's army? The answer is no imo. It is established some beings are demonic, some angelic (and even then Dracula has dominion) and some human (such as the Zombie soldier in AoS.) Not only this but some of the ID's such as faeries, and the evolution of some of the others are not fought in other games. If anything ID's seem to be more Akin to Alucard's familiars, most prominently the Faerie, Devil.
How about the enemies made of stone or natural organic material ? Stone (and wood golems), gargoyles, and in a couple of instances such as LOI Medusa starts off as a Stone Statue that comes to life. Maybe I'm reading too far into this, probably am. After all Medusa turns to stone at will, Gargoyles cloak themselves as statues, but ID's originate from stone but evolve into other creatures. (none of which I can remember actually turn to stone, but it's been years since I've played COD.)