No they're not, otherwise I'm sure dennis' list up there or the wiki I'm looking at would say so. Not to mention they don't even resemble the Ring Wraiths in appearance.
Well we know that dead men can't return to life in Middle-Earth, so surely that means that being a wraith is somehow different from being brought back to life, or maybe Tolkien's definition of 'brought back to life' is different from ours somehow (can't imagine what that would imply)..
That's the issue with catch all terms and movies. We can't compare the description of book-wraiths and the movie ones, either. Gorlim, the first recorded wraith, could have looked exactly as the Dunbarrow apparitions did. We don't really know. He is stated as the first instance of a wraith, yet has no malice or evil in his appearance, just regret which keeps his spirit attached to the world, like a certain group of men from Dunbarrow. That's why I've always believed the wraiths to be a relatively benign phenomenon before the Ringwraith corruption.
This is a subject to debate, Dunbarrow men were incorporeal but otherwise entirely wraith-like. The thing about LOTR undead is they come in a small variety of flavors. All undead spirits that continue to exist in LOTR are wraiths, basically. The Dunbarrow men being a weakest form of the appearance, being unable to physically affect their surroundings. Had Sauron known of the Dunbarrow men for a long enough period, I'm not so sure they would have stayed as incorporeal ghosts.
Even hinted at by the books and character themselves;
In The Return of the King, Gimli said, " Strange and wonderful I thought it that the designs of Mordor should be overthrown by such wraiths of fear and darkness. With its own weapons was it worsted!"
Chalk it up to ignorance of undead or fine insight by Gimli, that's the fun.
Especially since being 'undead' is such an odd concept in LOTR, what with persistence of spirit with the motivation of their lives still being held. That's about as alive as anything can ever be. It could easily be stated that the Dunbarrow men were a weaker form of wraith, sans Sauron manipulation. We don't actually have any reason to believe wraiths were anything besides ghosts until Sauron created the Ringwraiths.
The Dunbarrow men being immortal without ring intervention is the odd one. It could be assumed honour-breaker curses are stronger than mortality in LOTR if they are forged by strong enough people [or old enough..? Less removed from the divines back in the first ages, as well, which would explain the strength of their residual magic in comparison to Fourth age+ magic].
And it wasn't his possession of Talion that made him become a wraith or what makes him undead, which is sort of what it sounds like when you put it that way. I'm pretty sure he can exist outside of Tallion since he's been a wraith for hundreds of years by the time they're thrown together. Tallion was going to die and then he was possessed by Celebrimbor for some yet-to-be-stated reason which prevented his passing, and at that point they're inhabiting the same body (lord knows why since a wraith shouldn't need to piggyback some other mortal in order to manifest physically and affect the world, especially one as "powerful" as he).
I'll put my money on Tallion being a far-removed descendant or some such, just to shoehorn in real connection between the two.