If it’s a 200A transfer switch on the load side of the 200A service disconnecting means, I don’t see why it would need to be fused, especially if its service rated and sized for the full load.
I don’t see anything the NEC that would require it either and I have never been required to install a fused transfer switch on a residence before. The generators I’ve installed all had their own built in OCP, which was rated lower than the maximum rating of the transfer switch.
