>>327632136
How you would do this is by attaching a HTC tracker to the cat and then having a cat model in game attached to a hip bone or something. hen the cat moves around it'll move the bone with it and the cat model attached to the bone will move around in VR with you. 
In VRC this is a fucking pain in the ass but doable. It might be doable to hack it so the cat gets his own account... but you'd need to run VRC twice. 

In other social sandbox games this is easier.