How is that observably different from backwards causality existing? Perhaps we need to taboo the word "cause".
It seems very intuitive to me that being very good at predicting someone's decision (probably by something like simulating the decision-process) is conceptually different from time travel. Plus, I don't think Newcomb's problem is an interesting decision-theory question if Omega is simply traveling (or sending information) backward in time.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
(I plan to make these threads from now on. Downvote if you disapprove. If I miss one, feel free to do it yourself.)