A few pages of posts before yours is a post describing the quirks of the Coast Provines's becoming part of the Republic of Kenya. IIRC, the courts there were not the standard English derived affairs, but were islamic in nature.
Views were divided as to whether the coastal strip should be treated as a single entity with Kenya Colony, or whether it should be handed back to the Sultan of Zanzibar or it be treated as an independent entity and declared Independent.
In a report submitted to the British Government and the Sultan of Zanzibar entitled The Kenya Coastal Strip Ð Report by the Commissioner Mr. Robertson recommended that the coastal strip be incorporated into Kenya before self government and independence subject to certain safeguards being given to the coastal people which should be entrenched in the constitution.
... Robertson further recommended that the British Government abrogate the 1895 Agreement with the Sultan of Zanzibar and that another Agreement be made between the Government of Kenya and the Sultan of Zanzibar whereby the Sultan of Zanzibar will surrender his Sovereignty claims over the Coastal strip in consideration of the Kenya Government undertaking to respect and safeguarding inter alia the maintenance of the Sharia Law for Muslims and the retention of the Kadhis Courts...
On the 5th October 1963, the said Agreement was actually executed in the form of an exchange of letters between the Prime Ministers of Kenya and Zanzibar Messrs Jomo Kenyatta and M. Shamte respectively.
Although I recognize it as speculative, it seems fairly likely to me that they were married in Kenya. His tribal area was on the other side of the country. So I doubt the agreement had much impact.
On the other hand, the issue does cause you to think about what kind of marriage they might have contracted (civil v. tribal v. islamic). I have thought it might be productive to look at the records in Kenya to see if there is in fact any indication of some legal ceremony there.
I haven't paid much attention to that because it seems pretty clear to me under US law that they would be held to be married for purposes of the citizenship law which is the primary substantive impact of the issue.