The SRH is basically a scaled up GP100. The Redhawk is a different design. Similar in some ways, admittedly, but pretty different in other ways. The lockwork is not the same even though there are some general similarities. The SRH gives a little more leeway in terms of smoothing the action, but obviously the demand for the Redhawk has stayed strong enough to keep it in production even though the SRH has been around for decades now.
I have an SRH, and even though I like it and it shoots well, it is an ugly gun. I have owned it for years, but I still don't care for the look of the round barrel in the square frame extension.