GMs are a group of staff that are dedicated to firstly keeping the game interesting and dynamic by hosting in-game tournaments/events and forum events. More recently their role has spread to provide in-game policing, for example dealing with farming cases.
Uniteam is group that has split-off from the GMs to deal with keeping the game appealing and un-overwhelming to new users. They do this by server sitting and hosting tournaments exclusively for new members.
GMs are higher than Uniteam. GM have full in-game moderation privileges and banning ability, whilst Uniteam an unofficial staff team have limited in-game moderation abilities.