Yes that's right and I realized it right after I posted it.(Silly poster!) Of course it all would have melded into one big hunk of evil and it wouldn't matter if it were the ring, Sauron, or Aragorn. It's all really Melkor.
Except that Melkor is no longer a personal presence in Arda, having been expelled into the outer dark. However, the discord which Melkor originally wove into the Ainulindalë continues to be manifest in Arda. So, in an impersonal way, one could say that it's all Melkor. Tolkien's myth does not have persistent, personally evil figures analogous to Satan. Melkor is pretty close, but he is dispatched well before the End, so he fails to map completely.
What Tolkien really gives us are series of "Satan figures." These guys keep coming to bad ends. Perhaps this is a deliberate attempt to avoid equating any being with Illuvatar, and thereby falling into dualism.