We are talking about SPARC ADI, still sold by Oracle and Fujistsu.

https://www.oracle.com/servers/sparc

Linux while not being UNIX, does support it as Oracle upstreamed SPARC ADI support during the brief time they had Oracle Linux support for SPARC.

https://docs.kernel.org/arch/sparc/adi.html

Now why someone would use unsupported OpenBSD on SPARC for the kinds of clients that pay for this stuff, beats me.

Assuming it does even support SPARC ADI.