As long as you spend NX in Vindictus it will count towards the promotion. If you use NX to purchase a gift, it will count towards your spend tier (not your friend). The amount spent is accumulated across all servers (if you spend and play on more than one). So for example, if you want the outfit on all the servers you play on, you do not need to spend that much individually on each server - it's a total across all servers.
FYI, you don't need to pick what server the reward will go on, if you have a character on, let's say, both East and AUS, then you will get rewards on both those servers. All the items are account bound and can only be traded within the account.
Protip: The Outfit and Tail come in a box, once that box is open it will become bound to character - so make sure you watch out for that once rewards are delivered.
I'm Sumirei, new to Vindictus team. I'm currently playing Vella and having fun (also currently taking the carriage between Colhen and Rocheste A LOT). I'm excited to be here and will have fun reading through all the posts and getting to know the game better~