I assume the scenario is working properly? I'm afraid that I never got the chance to test it past season 3 because I wanted to get it out in a reasonable amount of time (the turn lengths are long, but may be shorter now that a python exception is fixed since the version I first put out 5 months ago). About 10 turns into season 6 the following should have happened:
4 Dominion Unit spawns, Dominion taking control of initial cities that flipped to the Maquis that were not yet captured by the Federation or Cardassia (with the death of the Maquis), Dominion/Cardassia declaring war on Federation/Klingons, and Damar becoming leader of Cardassia.
After that, you should be able to build the Prometheus, the Romulans should enter the war with a unit spawn (you should also be able to build spies on this turn), the breen should enter the war with Broca becoming leader of Cardassia and you should get some Cardassian units (to simulate the resistance), and Thot Pran becoming leader of the Breen. Now for the conditional events:
-If Cardassia is captured and it is turn 177 or later, Cardassia will switch sides (note: if Cardassia is captured and retaken before turn 177, the game will not make them switch sides)
-If the war is still going on after turn 181 and Bajor has more than 4 cities, they will enter the war
-If Cardassia is captured and the Federation, Klingons, and Romulans have 10 or more cities combined on turn 180, the Dominion will surrender and either the Federation, Klingons, or Romulans will get a conquest victory based on number of cities (Cardassia can be captured after turn 180)
-If the Federation, Klingons, and Romulans combined have 3 or less cities, the Federation will surrender and either the Dominion or Cardassia will win a conquest victory based on number of cities (Cardassia can't win if they have switched sides, though)
I'm pretty sure that all this works fine as it's similar to code that I have tested (I somehow managed to test the Klingon-Cardassian war events without actually playing that far in)