Well it's not only the cameo of Zena Sempai and Moa from Ultraman Geed in Kamen Rider Saber Episode 16 that is related to Ultraman Series. First of all the screenplay for this episode is by Keiichi Hasegawa who had largely worked on Heisei Ultraman Series from Tiga till Ginga, then comes Koichi Sakamoto the main Director of Ultraman Geed, now currently streaming Ultra Galaxy Fight: The Absolute Conspiracy & many many more which you will be already aware of.
Adding to that, Hitomi Hasebe who had played Mizuki Koishikawa in Ultraman Max and also Lumina Igaguri in Ultraman Geed appears as Editor in chief Yuki Shirai for Monthly Grimm where Mei Sudo also works.
Yuki Shirai is also one more person who can see the Wonder World. She thinks it's because of the stress and she decides to go to camping. That's where Legeiel inserts the new Alter Book inside her which turns her into Yeti Megid.
That's not all! There is one more.
You might not recognize this person. But he is of course connected to Ultraman Series in a different way.
Even I & many might have thought that he is a just a side character. But he wasn't. He is the grandson of Eizo Yamagiwa who had Directed Return of Ultraman, Ultraman Ace, Ultraman Taro and Ultraman Leo. His name is Kaito Yamagiwa.
He started his acting career after getting aspired from Heroes. The person in charge of casting casted him something like an easter egg after the appearance of Iwata family and Hitomi Hasebe was decided.
Just wanted to highlight one more point. The person who edits the Kamen Rider Web for Kamen Rider Saber Episode Updates had referred Ultraman Series with references without actually mentioning the Ultraman Series.