I had the same error, but for P2 in a SQL server 2005 installation. Don't know what is your base installation, it would be good to know.
I'm not sure, but i think that the HPOvSdSnp is the one that installs the database structure, besides, it seems SD uses several methods of installation. So HPOvSdSnp is successfully installed in the subsecuent processes.
We tried SD 5.1 P1 & 3 on a windows server 2003 SP2 on a Oracle DB.
HPOvSdSnp installs a DB snapshot. It seems that it's linked to the creation of the DB bacause we don't have the error when we upgrade a DB. So maybe he tries to do an integrity test on the empty DB which fails.