Some of the staff have deemed it ILLEGAL or AGAINST THE CODE OF CONDUCT to ban the staff team in custom matches. There may not be a specific rule against the use of triggers to disallow players inside a match (especially since there's a trigger action to kick players), there is an out clause in the Code of Conduct.
The Plazma Burst Community Staff (Administration/Moderators/Support Members) reserve the right to ban, block, suspend, or otherwise prevent any player from using any service of or related to Plazma Burst for any reason at any time. This applies to the game, site, chat, forums, site messaging service, and forum messaging service.
Personally, I don't think enforcing a punishment based from an out clause and not based from a specific rule is fair for the community especially when the rules are laid out or made specific so that it may serve as a guide for the community to follow especially when kicking players out of a match is literally a game or a feature of the ALE.
There still needs to be a discussion about this with the staff especially from Eric who made the trigger function. However, I agree with Shroom that banning players or staff from a match shouldn't be considered against the CoC because there are still a lot of work-arounds for the staff to do. I would only agree for this to be against the rules if there's no way for the staff to moderate the game anymore. But, I wouldn't oppose if the staff decided to add it in the CoC.