I believe that is correct.
I've been able to get random ones to spawn by creating an erroneous entity for them--not that this helps anything.
But what I and the OP don't seem to be able to do is get the DefaultMinorFaction to ALWAYS spawn on a particular planet (despite tweaking other variables).
Sometimes it does, sometimes it doesn't.
I notice on of the default maps (I forget the name now) has a scenario where each player starts in a small cluster of worlds and each of them (one for each of 6-8 players) always has the designated planet spawn every time.
I've not been able to duplicate that.