See bz1014166 for an example. One of the tables was not created, error is logged in the log file yet installer consider the installation to be successful. Such an error should be detected and reported to the user.
The installer reports errors in the DB creation only when the build.xml reports a failure; the issue in bz1014166 was simply sql not being run. The other errors seen are "normal", such as tables not existing and things like that. Stephen can explain more about this.
Verified in ER7