I wish I could give you a positive absolute answer. The answer is 'maybe'. Supposedly livebearers will get along with bettas. However when I look at them most livebearers resemble bettas enough that especially with the fancy ones I'd worry about the betta thinking of them as rivals and with the classic blacks that they somewhat resemble betta females and might get attacked as well. Then again some swear by bettas as good community tank fish. I'd have a backup plan to remove the betta to somewhere else, either get a smaller tank just for him or plan to give him to someone else who wants a betta and will look after him decently.
My bettas, the aggressive and the docile, all live quite well with otos. I had disaster with Emma and the other female Bettas and Cories. I would seriously worry about any fish that had long flowing fins like the black mollies do. It may work if you have a quiet betta but if you happen to get one who is aggressive and territorial you will have a problem.
I do not worry about the otos. They are very quick little fish and do not get overly nervous. The bettas ruffle them up occasionally but they settle down and go back to sleep or feeding almost as soon as they stop swimming. It also helps that the otos are mostly night time fishes and they do not do much challenging of the Bettas during the day. They are more curiousity objects to the Bettas in my tank. Alex goes up to one of them and puts his nose on one of them and they swim away and he goes after it just for the chase. The oto goes back to the same spot and goes back to sleep and Alex is done.