My cable provider has a Roku app that acts as a STB. I can access recorded content, schedule recordings, etc from anywhere inside my home network. When I head up to a second home in the mountains and attempt to use the Roku as a STB, it detects that it is no longer on the local network. I'm thinking I could create a VPN between my two openwrt routers to enable the Roku to "see" my local network which has the DVR on it. Would OpenVPN be the right choice to enable something like this? Am I missing anything?
This is a very common use for OpenVPN. At home, you run a server. When your client connects through it from another location, the cable service sees the requests as coming from your home IP address and grants access.
Agree with @mk24 and just wanted to add that Sling, YouTube tv and Directv Now all allow streaming off your home network without having to use a vpn in case you wanted to check them out (there may be others that also allow it like Playstation Vue but I haven't tried or looked into them).