User blog comment:B214/Question and Answers 6/@comment-185.112.105.215-20161228104658/@comment-10330822-20161228123253

Pretty much, at least the high school portion right now. Both of the presidents of the ORC and Student Council are his servants, and the only other High-Class Devil on campus is also his servant, Ravel. On top of that, he has influence over all the other devils in those two groups as a result.

Rias is still technically there, she's just in the college portion, but if he marries her within the next year he could have complete control over the Academy.

Typical decorum from a class system/nobility stand point also means that he rules over all the devils that are below High-Class Devil status period, short of behind maybe their masters. He probably also has the same nobility status as Rias since he is engaged to her and if he married her he'd be a heir to her father's dukedom just like her. Also, Rias stated that all of Kuoh Town is under Gremory control, meaning that if Ise marries Rias, he'd gain control over Kuoh Town as well.