Bloodwhetting is bugged or the tooltip is incorrect
The tooltip for Bloodwhetting states "Converts 100% of damage dealt into HP".
Despite this, no healing occurs when you use Onslaught or Orogeny. At first one would assume you don't heal because the abilities deal damage to yourself, but that shouldn't be true either. Despite the HP cost being more than the HP you would heal, you'd still get a partial heal. Looking at the combat log, the damage dealt and HP restored are separate instances, which should also show for both off the off GCDs, but it does not.
So either something is wrong or the tooltip needs to be rewritten which is odd, because the PvE version of Bloodwhetting already specifies that it only applies to weaponskills.
I can only go off the English translation as I can't read any of the other supported languages so I have no idea what the French, German and Japanese tooltips say.