Well then, make it both, a contacts and a resources roll, if you like. Resources let's you buy things, mercenaries sell their services. I think that makes it a straight resources roll. If you don't know someone, you'll need contacts first, to find someone you'd want to hire. Other skills (presence for example) could also work for the summoning.
But resources is a fairly abstract thing in this game, and is therefore subject to skewed scaling. You'll still need a body to reanimate in the first place, and it is always possible that your "money" was not well spent, if the body and matching spirit is not all that powerful. Also remember, that you need a drum to keep them under control, and while a book drumming against your leg might be enough for two or three zombies, I think you'll need a larger one to control more of them (or be that much better at necromancy). That can all be done by compels very easily.
Not to dismiss your efforts, on the contrary, I admire them, but I don't really like those detailed summoning rules. To me the bargaining and uncertainty of a summoning belong very much to the setting, and an easy summoning rule like that can do that pretty good. The detailed summoning rules are great for building a golem or something like it, a magical robot, if you will. But even there, I would probably just make it a craftsmanship replacement or something similar. If you want to find just the right demon, you'd have to randomly summon a few of them until you found someone that matched what you are looking for. Much like if you where to go through a few applicants for a job. But on a zombie, you take the first one that is there in the flesh. Literally.