The RenderMan Menu is added to Houdini when the RenderMan for Houdini plugin is loaded.

If the top-level menu is customized to remove either the Help Menu or the RenderMan - RIS tool, the RenderMan menu tools will not be installed correctly. You will need to edit the <insertBefore> and <insertAfter> options in MainMenuCommon.xml to position them correctly in your customized menu.