At least for all the guilds I've talked to, Gruul's hurtful strike is now targeting the third person on the aggro list instead of the second. This bug is probably related to this morning's patch, because HS has been messed up with other patches before.
A possible solution to this problem is to keep your guild's best rogue second on the aggro list, and the actual offtank third. With hunters shooting Misdirections at the rogue and everyone keeping a close eye on threat meters, you should be able to do it.
(Thanks to Schleeze of Magtheridon for the solution.)