Board Thread:Naruto Discussions/@comment-35207441-20161115163133/@comment-25122992-20161115165109

1. Shisui is labelled an Anbu in the databook, so he is a one.

2. We aren't sure how often Shisui himself could use KA. It's very likely that 10-years limitation applied only to the Itachi's crow (all the non-Uchiha Sharingan wielders are limited in its use, and his Sharingan wasn't even transplanted to a human, but just to crow), also, there's nothing that says Itachi never used KA with the crow before this accident after his reanimation.

3. There's currently no reason to believe Shisui was somehow involved in Obito's control under the 4-th Mizukage. All of us can make their own theories on that matter, but as I said, there's no mention in the series about Shisui having any relationship with Obito, so it seems that they just never knew each other.