Notice the date - UBC 1997. This is the last version before it changed to IBC (which Caesar has options for). It's likely just in there as a legacy option.

Are you creating a new system or analyzing an old system built to UBC 97?

I don't know why an old UBC option is available for Wind but not Seismic; I'd guess that the code deffered to ASCE like the current IBC does for the most part.

If you're analyzing a system built to UBC 97, get a copy of it and read it for yourself. You shouldn't rely on checking a box in the software.