I think they can.
I mentioned one strategy I like to use is to build the Council of Esus, and, later in the game build HN Shadows. I send them out to the civs that are giving me problems or ahead of me in the standings and harass them by taking out weak units like Workers, Adepts, GPs (love that as the AI tends to stockpile GPs for Golden Ages!), etc. Then, as they get more powerful, I take out defenders leaving AI cities defenseless against barbs who raze or capture the cities.
A couple of related things tells me the AI knows who the HN Shadows belong to. I'm not sure if they should. I know if a HN Mercenary comes into my territory, I don't know who built that unit. The AI never builds the Council of Esus, so that would be the only way I can think of the AI could send HN units into your territory.
Anyway, consider this:
1. I have noticed relations deteriorate when I use the strategy above. Trade, border agreements, etc. are canceled. Why is that? Does the AI know the HN Shadows are mine?
2. Even more telling is this strange matter....When I check the diplomacy with the AI civ, I see the negative: "You razed one of our cities." Well, that simply is not true. I have never been at war with that civ. I didn't raze its city. However, as described, I took out the defenders with my HN Shadows, and then, the BARBS razed the city. Why pin this on me?
So the diplomacy is affected by what seems to be a phantom/untrue occurrence - that I razed a city. That could affect relations and may be the reason the agreements were canceled. Or, maybe the AI knows who the sneaky HN units belong to.
What do you think?
I mentioned one strategy I like to use is to build the Council of Esus, and, later in the game build HN Shadows. I send them out to the civs that are giving me problems or ahead of me in the standings and harass them by taking out weak units like Workers, Adepts, GPs (love that as the AI tends to stockpile GPs for Golden Ages!), etc. Then, as they get more powerful, I take out defenders leaving AI cities defenseless against barbs who raze or capture the cities.
A couple of related things tells me the AI knows who the HN Shadows belong to. I'm not sure if they should. I know if a HN Mercenary comes into my territory, I don't know who built that unit. The AI never builds the Council of Esus, so that would be the only way I can think of the AI could send HN units into your territory.
Anyway, consider this:
1. I have noticed relations deteriorate when I use the strategy above. Trade, border agreements, etc. are canceled. Why is that? Does the AI know the HN Shadows are mine?
2. Even more telling is this strange matter....When I check the diplomacy with the AI civ, I see the negative: "You razed one of our cities." Well, that simply is not true. I have never been at war with that civ. I didn't raze its city. However, as described, I took out the defenders with my HN Shadows, and then, the BARBS razed the city. Why pin this on me?

So the diplomacy is affected by what seems to be a phantom/untrue occurrence - that I razed a city. That could affect relations and may be the reason the agreements were canceled. Or, maybe the AI knows who the sneaky HN units belong to.
What do you think?