Normally, you could use any brand valves you wanted to, but these days, some manufacturers use a "custom" method of connecting their valves to their spout, and that limits interchanging them or even remotely mounting the spout. I know Price Pfister and Moen still use 1/2" copper between the components so you can mount the valves anywhere you desire and then pipe a single line to the spout. IF the spout has a "proprietary" tee at the spout, then you have to pipe the hot and cold from the valves to it individually.