Ascension, while it uses class ability energy, is not a class ability. Bungie, every so often, will allow it to trigger more things, there has been 2/3 times they've updated it since it was introduced with The Final Shape. First set of things were heavily restricted, they then did another update during Heresy to allow dodge effects, and then with Edge of Fate they allowed it to trigger things like HOIL, Gryfalcon Reserve Overshield, and leg mods such as Reaper/Bomber. Anything not being triggered is intentional. As for Ensnaring Slam, given their stance with Ascension not triggering Slice, its likely they don't want Ensnaring Slam triggering it either but BNGHelp will likely pass that on for clarification.