Well....it might seem like a bad idea, but in fact the MiCollab engineering guidelines have a deployment model they call "Network Edge" for the MiCollab server:
MiCollab has 2 NICs, one connected to the LAN, the other connected to the outside world. No seperate MBG required.
One version of this deployment model has the MiCollab server acting as the actual firewall for the site.
The diagram above might be right, or might be wrong - if you connect the MiCollab to the firewall instead of the LAN, then you will need to configure all sorts of firewall rules for the internal MiCollab stuff to work.