Vertica was C-Store, a column oriented store for analysis. VoltDB was H-Store, an in-memory database for very fast OLTP. (From testing VoltDB, it screams, and scales nearly linearly.)
I'm not sure HStore/VoltDB was a "spin off" of Vertica - they are quite different models fundamentally.
They use different architectures but there is a real organizational connection between the two products. I interviewed with the VoltDB team at Vertica's office.
I'm not sure HStore/VoltDB was a "spin off" of Vertica - they are quite different models fundamentally.