Isn't Khitmoer under Romulan control?
In the immediate aftermath of the Romulan attack, it wasn't under Romulan control - a Starfleet vessel was able to get there to look for Klingon survivors, and didn't have to get permission from Romulans, because that would have counted as "direct contact" which we know did not take place between 2311 and 2364.
Later on, we hear very little about the place. But in DS9 "When It Rains...", the first meeting between Admiral Ross and Chancellor Gowron is said to have taken place on Khitomer. Ross is in his apparent fifties; Gowron is of indeterminate age. For most of their lifetimes, Romulans would not have been letting either Feds or Klingons on their property.
So the meeting might establish Khitomer as being Klingon- or Federation-owned in the timespan from the Romulan surprise attack to the final year of the Dominion War. Or then the meeting might have taken place during that final war year, when Romulans would be allies, and might invite Klingons and Feds to Khitomer for old times' sake.
We just don't know for sure. We also don't know who owned the planet during ST6:TUC. Was it considered neutral in the UFP/KE conflict because it was a Romulan world? Or was the planet owned by those human-looking folks wearing green sashes and sitting under a green sunrise flag?