Guys,
Hope you are all aware of the fact that Oracle 8.x to 8i is just a upgrade and not a Migration. Migration is called only when you migrate from a base version such as 7.x to 8.x where there are lots of changes involved. If you want to upgrade from 8.1.5/6 to 8.1.7 then this is an upgrade and not MIGRATION. Yes, you have to install it on the same ORACLE HOME and run the upgrade script found in $ORACLE_HOME/admin/scripts dir.

Thanks