I imagine you want NUMA aware software specifically designed for multi-socket systems; off the top of my head the ones I've heard of are IBM DB2, SAP HANA, and Microsoft SQL Server — although I've had a chance to actually use any of them.
There was a study done recently that no major DBMS product can scale past 64 cores for similar reasons that Postgres can't -- too much contention on shared resources like locks.
Not currently for relational databases specifically as far as I know, though it is possible to build one in principle. The kinds of use cases and applications that really benefit from that kind of deployment hardware tend not to have classically relational data models.
Right, and at that point you should be using some sort of NoSQL anyway.
sql server scales incredibly well with the hardware but so does its price