No. But it isn't unheard of, either. I know UltraSeven used Capsule Monsters way back at the very dawn of the franchise.
Mebius and Decker also used versions of the Capsule Kaiju.
Cosmos was more about protecting kaiju than fighting them, so Cosmos had a recurring birdlike kaiju ally called Lidorias, and a couple of the other kaiju he protected returned the favor once ina while, though it wasn't a regular thing.
Ginga introduced Spark Dolls, Ultras and kaiju that were trapped in action figure form and that the characters could use to temporarily transform themselves into those Ultras or kaiju. Some of the supporting characters occasionally changed themselves into kaiju to fight alongside the lead when he became Ginga.
Ultraman X reused the Spark Doll idea and had the defense team create MonsArmors for X based on kaiju Spark Dolls, and eventually created a Cyber Gomora giant robot/kaiju of sorts that fought as X's ally. There's also Blazar's fiery kaiju ally Firdran (or Fadoran, phonetically), which turns into his Firdran Armor, similar to what Omega will use.
In fact, wasn't one of his capsule monsters Windom, or am I misremembering that?
Yes, Ultraseven's Capsule Kaiju were Windom, Miclas, and Agira in
Ultraseven and Sevenger in
Ultraman Leo. Windom and Miclas returned as Maquette Kaiju in
Mebius. Sevenger and Windom were two of the main STORAGE robots in
Z, and Windom, Miclas, and Agira all reappeared in
Decker. (The original Windom was a metallic life form rather than a robot, somehow. It was unclear whether the original Sevenger was meant to be a robot or a life form, but it was created by Ultra science.)