While it's theoretically possible it was accidental the first time it happened during the raid on Monday, people repeatedly blasted "DON'T DO THAT" (paraphrasing) in every zone-wide chat before the 2nd run that day, and it happened TWICE on that run, and then AGAIN yesterday. Plus the offender was confirmed by a GM to not be in the league and hidden from player searches.
But on the other hand, we have to actually be able to identify the griefer in order to actually report them. Sadly, it's really difficult (if not impossible) to identify a single person with a slightly different-colored name than all the people in the league amidst the mess that is a Hamidon run, and with the inability to find outliers using the /sea tool it's even closer to impossible.
I couldn't find the option for it but maybe I'm missing something...is there a way to add powers/effects cast by other players on targets OTHER than one's self to chat to identify the guilty party?