Sorry, I wasn't speaking to it being possible to bonus roll for the mount - only to it dropping on personal loot (as opposed to raid loot being set as *master looter*). There is no reason that I know of, other than class restrictions, that an item on a boss's loot table wouldn't be included in personal loot. (again, not speaking to bonus rolls)
And, according to wowhead, it will NOT drop on a bonus roll: http://www.wowhead.com/currency=1273...-fate#comments - scroll down for a list of known raid/world bosses that have a chance to reward mount on bonus roll, Gul'dan specifically states "no"