As far as I know, this isn't necessarily a contradiction to Tolkien's lore (which in fact contains more than LOTR lore).
Wraiths
do exist as well as a
Wraith World/
Shadow World.
As far as I know both concepts aren't so precisely described that there wouldn't be any room for "additional fiction" like in this game.
Again I don't see a contradiction. Of course it might well be that I'm overlooking something… I'm not a great expert in history of Middle-Earth.
Well just a few things
Aside the thing of a wraith leaving free will to the body it posesses.
How does the Wraith save his life or snatch him from dead ? I'm unaware wraiths being healers.
If he was already dead, how is his spirit still there, gift of men and all ?
And if he died a horrible enough death or is vengeful enough to not have his spirit leave, how is he not under control of sauron ?
It's also somewhat odd that for convenience purposes the Wife and kids were stationed at the black gate with him.
(I'll assume he's a Ranger of Gondor and not a Dunedain)
Second part is much worse though, Time slowing, Flamebinding to the floor, Teleport mind control ? High magic isn't exactly Lotr, especially in the 3rd age, and even Ringwraiths can't do that stuff.
Also I'm not sure about the whole mind controlling by the good guys, Tolkien was always pretty black and white about his good and evil.
There will probably be more down the line and sure it's not directly contradicting and will be explained away somehow.
The whole setup seems to fit much better in a setting like D&D though but the LOTR stamp is better for business.
Didn't those guys make Guardians of middle earth too ?