"Under Geneva to be considered a lawful combatant- either civilian militia or military, you must wear a uniform OR identifiable insignia, or be carrying arms openly to set yourself apart from unarmed civilians."
No. It's not "or." They have to fulfill all of those requirements and more:
Geneva Conventions
(2) Members of other militias and members of other volunteer corps, including those of organized resistance movements, belonging to a Party to the conflict and operating in or outside their own territory, even if this territory is occupied, provided that such militias or volunteer corps, including such organized resistance movements, fulfil the following conditions:[ (a) that of being commanded by a person responsible for his subordinates; (b) that of having a fixed distinctive sign recognizable at a distance; (c) that of carrying arms openly; (d) that of conducting their operations in accordance with the laws and customs of war.
http://www.globalissuesgroup.com/geneva/convention3.html#4
If they don't then, if captured, they simply aren't guaranteed the protections agreed upon under that Convention. Status as a lawful or unlawful combatant does not seem to be defined in that Convention.