I personally have not used Unity for virtual production but it definitely has been by others. However, in the past several months that I have been learning virtual production, it does feel like most of the focus is on Unreal.
Epic seems to really be embracing this as well and partnering with companies like Quixel to bring extremely high quality assets to their users for free. Quixel has a ton of photogrammetry assets that they've captured around the world.
Unreal also offers free access to its metahuman creator for free which is amazing if you want realistic 3D characters.
https://www.unrealengine.com/en-US/digital-humans?sessionInvalidated=true
I've also seen some mocap platforms start to focus on better connecting their software with Unreal and specifically its metahumans.
In my short time learning all this, it does seem like you are going to have access to more assets, tools, and tutorials if you go the Unreal route. However, I'll let someone more seasoned chime in on their thoughts. I'm still new to all this myself. 😀