I believe how it works is the skeletons have two sets of hate persay. It has its own hate, and it has the hate linked to Vrtra. It goes after whichever hate is stronger. So if the PLDs have a lot of hate on Vrtra, even after t4 nukes it'll keep running for the PLD. However, after Roars/Deaths/whatever, when hate is usually very light, often time the Skeletons will turn towards you once you do one Thunder IV. So from my experiences it works that way, with the mob going after whatever has more hate, the action against it, or Vrtra's shared hate.
Edit:
Suiram's trying to develop a new strat that'll decrease the amount of people needed for Vrtra and try something different, which might turn out better. Nothing wrong with looking for new information for new strats, if no one did we'd all still be using PLD/WAR AA rots and SC + MB on every HNM these days.
who for real cares? uve killed vrtra, right(k, kupo). nuke em out b4 u bother to care.