Yes, wiki cites 300k per hit for Svalog's nuke.

As for whether elemental resist buffs improve your affliction resistance... anecdotally, I feel like it does slightly. Nowhere near reliable and it takes a large sample size to notice. But for example, over the times I've joined dark ult raids, I've noticed slightly better odds of resisting both poison and corruption in a given turn with Sacred Conviction (Michael's light atk/dark resist buff) active compared to not.
But it's nowhere near enough to justify using such buffs explicitly to resist afflictions. It's a minor perk in addition to whatever the main reason you use them for.

As for whether Barong's passive helps? I can't say for sure. The one time I paid attention was for St. Nicholas guild order when I just didn't have an Anubis available at the moment (also that was during the time when a bug allowed elixirs to be used :P). So a very small sample size suggested to me that yes, double Barong helped a bit more than Barong + Anubis.
Other than that? I honestly just haven't really paid attention to the difference between Barong + Anubis and 2x Barong for dark ult. Which probably implies that if there is a difference, it won't be big if I can't casually pick up on it.