Kamen Rider OOO takes out three Showa-style arthropod kaijin and Dagon from Magiranger - all very close analogues to the black Core Medals from Movie Wars Core and Kamen Rider Poseidon from Movie Wars MegaMax, both involving OOO.
As a part of their declaration of victory, Silva announces that he detects no Riders or Sentai anywhere, despite Don standing just a few yards away. Proof of Don's Butt-Monkey status? Maybe...but then you realize, he's out-of-costume, so Silva's systems probably don't register him as GokaiGreen.
Silva kinda forgot about the Go-Busters and Fourze as well but the point is that Silva probably can only detect in-costume Riders and Super Sentai warriors and not the out-of-costume ones.
It's a little scary to see The Joker Undead among several other members of Dai-Shocker, especially if you consider that it might be Kenzaki being the Undead. Thankfully there's the Decade interpretation of how Joker was born.
It dips into Heartwarming in Hindsight, as the stated mission of this Dai-Shocker is to defeat Captain Marvelous' Dai-Zangyack Empire, which is going out and killing Kamen Riders. It would make sense for the Joker Undead to try and save some of his friends who just happen to be Kamen Riders.