“We are so grateful to Mr Joe Citizen and Ms Jane Do for their generous donation to our Winter Appeal”. Are they married? Maybe. It’s clearly a joint donation. Is it relevant to ensure their legal relationship is exposed, or may that simply be inferred from their name as per your example?
Yes. When husband and wife have different last names, the relationship may not be readily apparent, however, while “Mr. Joe Citizen and Ms. Jane Do” is a perfectly acceptable way to address correspondence, and would be perfectly acceptable on a list of donors, it’s not sufficient for the type of article the OP is writing.
Think of it in this way. If you attended a fundraiser for an organization and I was introducing you to this couple, I would not perpetuate the ambiguity created by maintaining different last names.
“I would like to introduce you to Mr. Joe Citizen and his wife Ms. Jane Do.”
And I would offer some basic information or points of interest to encourage conversation.
“Jane is a Research Fellow over at the University and a contributing editor to the Star Journal. And she’d never tell you this herself, but she has the most beautiful garden in the entire county.”
That is the type of article this should be…a basic introduction, in this case to the reader in which you take the opportunity to voice your appreciation for what is most likely a very sizable donation.
The fact that this is a same sex couple should make no difference. It should be handled no differently.
“Rau, I’d like for you to meet Mr. Joe Citizen and his husband Mr. Steve Public,” etc.
There’s no implicit approval of the marriage in that statement because it’s just a statement of fact. Introducing them simply as Mr. Joe Citizen and Mr. Steve Public, leaving out the word “husband” or “spouse” would however indicate my disapproval of their relationship because I would be refusing to acknowledge something that is just a fact due to my disapproval. It would be incredibly rude, which is why, as the OP said, the boss is insisting it not be omitted.