I just encountered the same problem.
Stopping SAPINST and adding SAPDATA_HOME to root's environment didn't fix the problem.
But adding SAPDATA_HOME & ORACLE_HOME to orasid's environment did fix it.
It seems that these should already have been in place (by SAPINST),
but this error occurred on the Install DBA TOOLS step.
Evidently, the installer hasn't setup orasid's environment yet at this point.
Resolved.