[PvK]

Yes, Iron Faith requires Drain of at least 1, which subtracts from the research speed of Black Priests (unless you have them research someplace outside your dominion).

Although this is a disadvantage, it's untrue that this makes it impossible for Ulm to keep up with research. Ulm is great at forging cheaply, and there are several items which give research bonuses, and which stack together. Quills, skulls, black lanterns are worth 3-9 research points each, can be stacked two per researcher, and cost zero gold and zero to maintain. Forged by a Black Priest using a Dwarven Hammer, they don't cost many gems, either.

PvK