Aizen doesn't need to see something to be aware of it, he was aware of literally everything Ichigo did over the course of the first half of the manga despite not being present for any of it, and he clearly implies that he knows how Ichigo's battle with Ulquiorra went.
Either way, it does not change any of my other points, Ulquiorra is definitively put below Yammy in every single comparison made between them, manga, databooks, novels, everything.