I decided to test this instead of just assuming from memory, because i was quite certain about it. Here are the results.
Sinope from turn 1 to 30
Turn 1 - initial garrison
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Turn 2 - peltastai logades
http://prntscr.com/lao8jd
Turn 6 - hoplitai
http://prntscr.com/lao8wp
Turn 10 - xystophoroi
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Turn 14 - hippakontistai
http://prntscr.com/lao9hi
Turn 18 - hoplitai
http://prntscr.com/lao9su
Turn 22 - hemithorakitai
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Turn 28 - hemithorakitai (probably in turn 26 but i missed it)
http://prntscr.com/laoacf
Turn 30 - peltastai logades
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Turn 30 - Government Overview
http://prntscr.com/laob5v
What i noticed is the following.
- The rebels from Sinope are recruiting from the settlement, not from mercenaries. I made sure to recruit all mercs myself leaving none available, plus the type of units recruited show that mercernaries were not taken.
- The rebels are recruiting from the polis building, and not from the eleutheroi government. Again this is shown by the unit type of the units recruited.
- The rebels were "encouraged" to recruit by parking a stack in their territory, however i have seen this behaviour regardless of using this trick. I just wanted to show clearly that the rebel AI does in fact recruit, contrary to what has been stated here.
My conclusion is that the rebel AI is only capable of recruiting from the polis building and not the government, the only difference between those i can think of, is that the polis building is of hinterland type (indestructible), while the government is not. Therefore a possible solution i suggest is to put all the rebel recruitment into the province "building" (where the description of the region goes), as that is a hinterland type building, and see if the rebel AI is capable of recruiting from there.