I believed this megaevent was only in TA because I didn't have it (over 200 DA games) since I played GalCivII...until now.
I got them again today! (DA metaverse).
This time (from what is visible to me) they are not attacking me anywhere but they are attacking everything else. Consistent with the megaevent message, they are attacking ships outside their own combat zone (about 50% of the other races' planets are within my own territory; those are being attacked too).
(EDIT 28Mar2012:) later in the same game...
I guess they don't have an economy so I didn't try to take their economic treaties. I didn't need to get them to attack anyone, but it seems they are "at peace" with me. Eventually they settled for giving me 256 BC! Surely the worst possible begging diplomat?
I think they will be back because in my current game the Drath also keep begging help which I now repeatedly reject.