Not sure if this has been stated anywhere yet but to make an Allied Race DK on the PTR currently it says that the purchase of Shadowlands is required. (Which I did purchase already but I guess it doesn't count for the PTR) I guess this kind of makes sense since it's kind of an expansion feature. I'm guessing that they're not going to be available in 8.3 but at a later date. Maybe 8.3.5 or even the prepatch like DH before Legion.
Edit: Well I just saw a post on Wowhead literally seconds after I posted this that says this info lmao
Edit 2: Also side note, are they going to add any undead textures like the original races have? Like the 3 undeadish faces and 3 different skin tones and hair colors.