Can a low-bitrate BluRay video be written to DVD-R to be played by BD-players?
Almost all Bluray players will play a UDF v2.5 with a movie on it, even if the physical media is a DVD.
Another twist is to encode the movie as AVCHD, which was originally meant for HD camcorders recording to DVDs. Many DVD (!) players and all Bluray players are compatible with this format, so if you encode your movie in this format, you have the unexpected benefit that it will work not only in Bluray players but in many DVD players, too.