I've kept a dwarf Gourami the same way. It did have a couple frogs in there too.Good question. I have previously kept a Blue Gourami alone in a Walstad style 10 gallon before. No issues. Gouramis and Bettas are both from the "Labyrinth Fish" family.
When my Betta died I'm wanting to get a dwarf guorami but I'm not sure if they can live alone