Raid battles have nothing with union: its just like the raids we have now: you start battle, you can ask for help (or not ask, if you confident you can solo) and u beat the living sht out of poor boss. Union event on the other hand is different and im not too familiar with it: it has some sort of personal contribution, union contribution and whatnot. Basically if you want to get max profits from union event, you need an active union. But for raid event you dont need any union.