Yes, the Permatex Ultra Copper product is a silicon product. One of its suggested uses on the label is exhaust flanges and manifolds so I gave it a try. The FSM suggests that no sealant at all should be used on the manifold gasket but I have tried that with not so much success. The manifold gasket is pretty stiff, and the torque available is limited as discussed.
I am not familiar with the Copper Kote product but will probably give it a try if the silicon fails and I have to do it again.
Peter