Theoretically Inf supports more than 2 teams (the setting MaxTeams in InfilTeamGamePlus will do the trick for TDM).
Unfortunatly it will most likely be unplayable.
First the spawn points on most maps were designed for 2 teams (can most likely be circumvented with RTS)
Second, as far as I can tell there is no way to set up a camo for the third/fourth team. During my quick local server test, the third team always started with the TeamA camo.
Third, the only ways to get into the third team is via team balance or a manual change to the InfiltrationUser.ini.
And last, the scoreboard doesn't support display for a third team (maybe no big deal, but that way one third/fourth of the people on the server will stay hidden)
If you are still willing to try, good luck
