In answer to the OP, both. Remember this exchange between Harry and Cowl in Dead Beat?
Harry - "I don't get it," I said. "I thought that you guys hated one another's guts."
Cowl - "Oh, yes."
Harry - "Then are you working together or trying to kill each other?"
Cowl - "Why, yes," Cowl said, and what sounded like a genuine laugh bubbled in his voice. "We smile at one another and play nicely all in the name of Kemmler's greater glory, of course. But we are all planning on killing one another as soon as it's convenient."
I think Kemmler and Drakul's relationship was similar, though probably lacking the personal animosity Cowl and the other necromancers had for one another. There's no way Drakul couldn't have seen Kemmler as a threat over the long-run. In the short and medium run of events their goals may have been compatible with one another's, but Drakul didn't get his position of power by being stupid or ignoring people who could hold power over him. Kemmler was crazy, so it's hard to guess what he thought about Drakul, but he had to know Drakul's reputation and probably thought about removing him at the appropriate time.