But is it having them on Dtube, or is it the Steemit post linking to it making the money? You could keep them on previously mentioned service, and monetize them with a post with description here. Previous service still works better than Dtube (which I find frustratingly slow to load vids), but doesn't monetize, like you say.
Its probably the post here linking to it, but still.....
But you are correct, Youtube will reward forever, so unless the video is a hit from day 1 Dtube may not really be a better option in the long run. Especially when you have youtubers making a killing off old videos