I have no experience in the field, but is it really that difficult to have servers on Xbox as opposed to everything else? I mean hell, some games fully support multi-player servers for all platform cross play.
The problem with cross console on private servers tends to come from the rules set forth by the company. Microsoft has a lot of restrictions on how cross platform multi-player can be implemented, and since the servers are being hosted by the players and not the company they most likely aren't able to meet the requirements.