Oh I was waiting for this one!
As I said for all the other races, NO CLASS LOCK, all races should be able to be all classes.
I'm gonna focus on giving all the understandable reasons I can to explain why "UNDEAD" can be Druids and Paladins in the next posts.
IF NOT POSSIBLE and you still decide to go full STEREOTYPE, then all classes except Priests, Paladins and Druids. If they can't be Paladins they shouldn't be Priests also.
Feel free to disagree after reading my explanations.
I say that if we have class exclusiveness with racial traits it should allow for justifiable reasons to play any class no matter the race, in addition, allowing a race to be one class makes no impact if players don't pick it, for example, if we have orcs able to pick warrior and mage, most people will pick warrior before piking mage but the option for those who want to play an orc mage is still there, so, 76% of orcs play warrior and 24% play mage. the only thing we could expect to make it some more lore wise it will be that trainers for mage or any other magical class will only be set on undead npcs at their capital so it will make sense that for an orc to learn new spell and complete class quest they travel to the undead capital in order to learn them.