Yes you can! Do note that the midnight is the more aggressive of the two and will probably chase the flameback around for a bit until they work out "living arrangements". I have a midnight and coral beauty in my 160-gallon and they get along great (it was only for the first week that the midnight chased the coral beauty around). Lots of hidden caves, holes and crevices in the rock work for them to explore is key foro keeping two of these together.
When I say "hidden" caves, I mean caves in the middle or back of the tank that only the fish can access and can't be seen directly from the front.
