Dwarf Gourami + Betta = fail?

Really, if you're concerned, I wouldn't put the fish on the line. They are very similar in appearance and genetics and every instinct they have will tell them to go after the other. A divider would be a much safer, albiet, less attractive option that would pose no threat to eithers' health. If you watch them VERY carefully, it could work temporarily, but if they shred each other the minute you aren't looking, I don't know that you'd feel too great.