Got all of that from http://www.swat-4.com/Yes, it is true. Thanks to experimentation by TacticalGamerz.com, 10 Player coop games are possible. However it comes with a price that some people may not be willing to pay.
Here is the process: Edit your SwatGUIState.ini file by changing all the necessary settings for cooperative gameplay and choose your maps. Next you must set the MaxPlayers=10 and then change the properties of the file to READ ONLY.
The big problem with using this workaround is that if you go into your server GUI and try to change any settings the server will revert back to the default max 5 players. According to the guys over at TacticalGamerz.com if your server is non-dedicated then you can change some settings using the console but unfortunately most console commands don't work on a dedicated server. With the this workaround you are forced to make server changes in the .ini file.
The other big problem is the obvious issue of server load. You may want to experiment what is best for your server because perhaps 10 players is too high of a number. You may have to limit it to 8 players or less depending on your bandwidth, etc. The size of the maps is also an issue. Some maps are extremely crowded with 10 players.
Thanks also goes to SAS_Trp_Noah and the SAS clan who also emailed that they too had made the same discovery. However TacticalGamerz.com was the first to discover this as far as I know.