I may be interpreting it wrong but Goenka says that vipassana is the ninth jhana, not that the ninth jhana is vipassana. I think the only intended meaning of this is that vipassana is more important than all the jhanas. But I'm not sure, as I've heard this a long time ago.
He turns his mind away from those phenomena, and having done so, inclines his mind to the property of deathlessness: 'This is peace, this is exquisite — the resolution of all fabrications; the relinquishment of all acquisitions; the ending of craving; dispassion; cessation; Unbinding.'
(Jhana Sutta - Thanissaro Bhikkhu translation)