You can start a coop server in UTF in game using the admin menu, when you do that, the map will also be changed to whatever is defined as 'StartMap' in the configuration (Vortex2 by default).
Alternately, you can start a server using UTF coop using the gameclass CoopGameFix - more details on how to start using the command line can be found on the Run/Start page of this manual.
Since you cannot choose difficulty when starting a coop server out of the box I highly recommend setting up a proper startup line.
The UTF coop game type is by far not as coop-specialized as JCoop or MCoop. UTF Coop was simply added as a convenience. You may find a few benefits running UTF coop, especially if you don't usually run a coop server and are very much used to UTF as DM/Team mod. Following is a list of peculiarities UTF coop encompasses...
As I said, this gamemode was added as convenience, and is not meant to replace any coop-specialized mod. However, people who usually run DM/Team and occasionally run a coop server will find this useful, because no other mod is required to be installed just for coop.
Practically you get the originally coop, without all the specialized features other mods have added to coop exclusively for cooperative play - however - you get ALL the admin commands of regular DM / Team in UTF, which is a lot! And maybe you are just going to like a simplistic coop mode which has the biggest bugs fixed...