Orcs in Morrowind, while not actually stupid, certainly have their intelligence allocated to parts of their brain other than those used for verbal communication. While they excel at war tactics and crafting, their tribal nature still shines through. For many, if not most, Cyrodillic (English) is used clumsily and their limited mastery of the language leaves other races assured of their stupidity. Orc voices should be deep and perhaps a bit gravelly. Tough. Delivery can even be a bit choppy and abrupt. Your voice should also account for the fact that orcs have huge tusks that get in the way of their speech. This would make 'S' sounds difficult. Esses would sound instead like Sean Connery esses, a little like 'sh'.