The HP schema extension utility extend the directory schema, which is a prerequisite to creating HP LOM objects in the directory. The utility is part of the directory support package.
You need to verify that the HP Schema extensions have been applied to the directory in order to create HP LOM objects in the directory. Reapply if you are unsure.
The directory support package also contains the MMC snap-ins that allow manipulation of HP LOM objects in MMC. One caveat: the snap-ins are currently English only, in such a way that they do not appear if the MMC was installed in a non-default-english language.
The directory migration utility can also create LOM objects in the directory; there is a GUI and a command-line (HPLOMGC) version.