They don't, the Dullahan in Skirmish will shield block Sudden Lunge, and the stun won't proc. Also, stun does land on that quest NM, but he resists it like anything BLU wise after a while. Can be subduction spammed/kited but will resist gravity after a while. Suggest if you do it as BLU to bring 2 and just kite/Subduction, as you should have him dead before he's full resisting. I could get him to 30-40% solo before it happened. Alternatively, melee+WHM or solo PLD, took me 22 mins as PL because Ingrid likes to drink and not do her job of dispeling his shield :/