I have a Roku Ultra, there is no newer, and I can control it with my Harmony IR remote. That said, I answered the question with the previous post.Newer Roku units use WiFi remotes. If yours is newer, it won't work.
If he had a Harmony remote there is no need to teach any commands any commands at all. Once you program the Roku into it they are all there. That coupled with the newer Roku remotes not having IR makes that impossible.If you have access to a hamony remote I don't see any reason why you couldn't teach the IR codes to the DISH remote.