There are so many missing xmls from the DLC folder it has to use some from the base game, Events, Blackholes, Artifacts, Encounters, Formations, Battle Behviours, most of the Diplomacy are all missing from the DLC folder.
Well AITechGovernorDefs is not one of them.
1) it does not contain Artificial Gravity or any other new tech.
2) I tried it by now. I could not get an AI to use TechGovernors via modding.
AITechGovernorDefs.xml is not functional anymore.
I haven't tried to modify that particular file, but I did notice a while ago it doesn't appear to have been updated with Crusade--which, I would imagine, would have to happen given the significant changes to how the tech tree works.
That said, did you place the mod in the GC3Crusade mod folder? Also, I think some people have had trouble with mods not taking effect in certain circumstances. IIRC, one recent problem was resolved by validating game files on Steam...
Those may be dead-end tips--the AITechGovernorDefs.xml may truly be nonfunctional. I don't know.