Just reached Yukash and got thrashed by the first group of Zhentrims. I forgot that the Zhentrim Terror Teams of Yulash are much larger than the Drow patrols of Hap. Also their mages are pre-buffed with Minor Globe and Prot Normal Missiles and cast Fire Shield as their first spell. So it's hard to interrupt their spell casting.
So I conclude that doing Yulash first is probably doable, but there is a reason you are supposed to do Hap first.
So I conclude that doing Yulash first is probably doable, but there is a reason you are supposed to do Hap first.