I definitely wouldn't put a dwarf cichlid in the same tank as a betta. Both dwarfs and bettas have a range of personalities, and if either of them takes a disliking to the other they'll probably kill each other. I was cleaning a betta tank and floated the betta in another tank while I worked on his tank, and the two were facing off the entire time. A. Cacatuoides can be just as aggressive as blue rams, especially if you get a pair.
Not saying it can't be done, but I certainly wouldn't do it. If you try, you'll need to have another tank set up so you can permanently separate the two.