it can "use" your MBG in the DMZ but you need to install mbg on the micollab in order for the solution to work properly. I may be wrong here, but I think MiCollab comes with an mbg and you need to cluster that mbg with your DMZ mbg so the licenses on MiCollab can be shared and so MiCollab configuration can be pushed out to the DMZ MBG via clustering.. Note that in this setup, the mbg on MiCollab doesn't host any sets, it's cluster weight is set to 0.
make sense?
