I don't have reference materials available, but I do note that as far as we see in the two main series, neither Prophecy spends time trying to "fix" the other Gods. To me, this is pretty good evidence -- anything that those two agree on has to be pretty solid. ;D
Side note. The Melcene people don't really believe in any of the Gods or Prophecies; call them ... "Cthragnostic" if you will. From their point of view, all those disciples and grolims &c are just wasting time.
Update: Inspired by @harry-johnston in comments, I did a little digging. I couldn't find the exact passage about "this world exists so you could stand on it", but I found references to it. As well as the drunken Arend whose entire purpose in life was to heckle Ce'nedra and get her past her stage fright. Add to that Belgarath telling Garion that if he'd lost to Torak fully half of creation would have "shimmered and vanished" and it looks like we have a more complicated vision of how much of reality is supposed to be there, and how much is there only to support the Prophecies' battling.
I'm starting to see this in terms of Venn diagrams... There are some people, planets, etc which are relevant to the light prophecy alone, some relevant to the dark prophecy, and some in the overlap zone (though with a different destiny in the different visions). Relevant to the actual question, we never see any hints that the Gods are only useful to one prophecy, or any indication that they would disappear if the Dark Prophecy wins. So I'm going to conclude that they are "real", where "real" means they are germane to both P's and will still be around whichever P wins. Now if that demon lord's "third way" had won out, everything is on the table.
Final thought ... if the Light Prophecy wins, will thousands of galaxies just ... disappear? That would reinforce the "us-vs-them" mentality Belgarath likes to talk about!