No? If you've read Umineko Yasu is literally used in EP2 from Shannon. Everything is perceived narratively in Umineko including the characters which is why magic scenes exist at all. Shannon and Kanon are shown as separate characters via the Narrative with Beato being the witch persona of Yasu and the closest representation in narrative of Yasu not by name.
It's a narrative trick. The same type used by Beato when she wins against Erika. It states narratively the introduction of Yasu in regular text, adhereing to Knox 1st via foreshadowing whilst also not showing Yasu in narrative. Everything has to be contextualized in Umineko and if you weren't such a brainlet you would've come to that conclusion.
I'll make it simple like Umineko would.
[Red]The criminal must be someone who is mentioned in the early part of the story[Red].
Also Umineko thread. [Blue] They are mentioned in EP2 by Shannon.[Blue]
[Red]But must not be anyone whose thoughts the reader has been allowed to follow[Red]
[Blue]As per above characters Shannon and Kanon are treated separately by the narrative and we only ever see them presented as such. Yasu as a character sprite is never seen so contextually we never see their thoughts until EP 7 as per Clair when everything is spelled out. Narrative trickery same as the rest of Umineko[Blue]