I've had various bettas in various community tanks over the last few years. I've kept long-finned bettas as well as plakats with other fish which include: veil-tail angelfish, various tetras (neons, lemons, cardinals, rummy-nose....) without any problems. I've also kept 2 plakats in a 4ft tank together with the other fish and had no problems. The tank was very heavily planted and the 2 plakats would pass each other in the tank, flare at each other then move along - no fighting.

Generally, bettas are only aggressive with other bettas and anabantoids. Other fish are far more likely to be aggressive towards bettas because bettas are slow swimmers. Don't keep bettas with livebearers unless you are trying to control the fry population - bettas will snack on the fry.