We don’t have a WoB either way. Personally, I think Amarams POV at the end of WoR points toward him not being in league with Odium at that point. He seems to be 100% Son of Honor at that point. And his prime motivation as a Son of Honor was always to bring the Vorin religion back to power, which had nothing to do with Odium.
My theory is that his guilt, along with the loss of his good rep made him very upset and filled with hate, both toward himself and others (mostly toward himself, probably) and that when Odium then came and told him of the Heralds and their betrayal, he turned because there was, in his mind, no point in keeping fighting for the false church. I headcanon this at his time in Thaylen City, but that is my pure subjective opinion.
Edit: I defenitely agree though, Amaram needed more page-time. Not giving him POVs is a mistake in my opinion. I would have cut Sigzil and/or Skars chapters to give some time to Amaram, but that is just me.