An appraisal report is supposed to identify the client.
"Client" can be more than one individual or entity. It sounds like you have two entities which are the clients for this assignment.
I'm not sure what the UAD restrictions are for naming multiple entities as clients, but it seems to me that for USPAP compliance, as long as the clients (all of them) are identified in the report, you are fine.
IMO, someone asking you to identify one of the clients and not the other would cause you to violate USPAP.
However, I doubt if there is something nefarious going on; the issue is the format-requirements for UAD upload. Despite the motivations or intent (good, ill, or neutral), if it were me and I had multiple clients for an assignment, each one of them would be named in the report as such. I don't think it is a big deal that only one name fits in the UAD space. I'd comment that due to the UAD formating limitations, one client only can be named in the pre-printed form, but that all clients are identified clearly in the narrative for USPAP compliance.
That's my take; someone else might see it differently.
Good luck!