They actually "migrate" characters over here from other country servers like that? That sounds super weird, since they might have all kinds of different things. They might have different item rewards for local events, they might have community events giving rewards we don't have and so on - and he just moves over here with potentially having all of those items? I think it sounds odd, and also as Pankreas pointed out - will he get double of all SP/AP from quests if he do them again? That'd be a problem in my opinion.
The Norwegian server closed down quite recently because of lack of players and the players that were left were offered to migrate to either the Danish (.dk), Swedish (.se) or the international server (.net). From what I've heard from players that migrated, if they chose to migrate to .net the world needed to have a full hall of fame so it wouldn't create an unfair advantage for the players that migrated.
Regarding community event rewards and other items, I don't think it's a big enough problem for it to be taken into consideration. Sure, there might become a duplicate of an event weapon or two, but how much does it really matter? Other than a few event weapons, I don't really think it differs that much when it comes to items. What would even the alternative to this be? Just take them away from the player that has actually earned it or not allow them to migrate?
The attribute and skill points should of course not be rewarded twice from quests, something I hope it isn't currently. If it's, then it should be fixed; but hopefully it isn't.