In general terms, Kyle is correct. Mixing anabantid species is usually a risk, depending upon species, and especially with Betta. Now, please don't jump on me for saying this, because it is merely common fact that you can ascertain from any reliable source.
Not everyone has multiple tanks into which they can move a problem fish, so when this sort of question is asked my initial response is always to provide the "norm" for the species. Fish are sometimes individual, as can be any animal, and this or that fish may not necessarily follow the "norm" for the species. The fact that you can walk up to a certain bear in the forest and have it walk away and ignore you does not mean you can let down your guard for bears in the forest. I run six or seven tanks in my fishroom, and over my 25 years in this hobby I have had problem fish that had to be moved, once or twice even given away or destroyed.
It is always safest to assume the norm for a fish, and ensure you can deal with the situation if it arises; if you can't, then please do not tempt fate. It is not fair to the fish if one or more of them decide to behave normally and become bullies, or worse.
Byron.