I think there should be consistency. Either both players get some way to maintain some level of salvage income on neutral planets (aka, something that can gather salvage independently of command stations), or neither player can (aka, when the AI loses command center, it loses salvage too, just like it does with us).
That said, I wonder if the new change for 7.036 (completed command station needed to gather salvage, regardless of any other salvage getting structures) applies to AIs too? If so, that would mean the although guard post count would buff salvage rate on that planet for the AI, it would lose salvage all together once the AI command station goes down, the same as it would for our Spire cities.
If so, that would mostly "fix" the issue.
Still unsure about the relation of the number of guard posts, difficulty, and command station type in terms of AI's net salvage efficiency on a planet.