The Yellowcap Venguard is linked to the note, that a certain amount of jhana battles have to be encountered before he spawns. I really have difficulties to get the Yellowcap Soldier to spawn in the heroic ramparts. Is it possible that there is such a restriction too? I'm doing a low BR run and on the other maps so far the circulation between rares was fair, but the soldier didn't show up even after around fitting 100 tries. It was always the Jamara who spawned. All other rares on that map were captured already.