Ugrak has a chance of spawning in any place an ogre raider does, i know this for a fact, i cleared all of the ogres ( including oowomp ), then he spawned in between the rocks, killed him, then he spawned again right after in a hut, then i killed him, the right after i killed him the second time he spawned a THIRD time, then he did not spawn again. First kill on him, i got the boots, second time, brandy, and the third time i got the bracers.