To answer that question...
It really depends on the temperament of the fish.
And a few other variables, such as size of tank, amount of cover/hiding places available and such. You can only try it and watch the results carefully.
I think alot of Betta people (my wife-n-I being such) would have to say in general, No
In the wilds they are able to maintain a wide berth of each other and keep their own territory.
Betta's are by nature and breeding aggressive to their own kind male or female, though females can be kept together with a minimum of fin shredding while establishing their pecking order.
Even then we've awoke to find a female thrashed particularly if the group is presented with a male in another tank.
Generally introducing Betta's together is done for fighting or breeding.
Lets not discuss fighting here, but mating.
Mating between Betta's is rough sex! Betta's are usually introduced in side by side tanks/bowls and allowed to observe each other while they both become more and more sexually aroused and ready to mate.
The male builds a bubble nest and shows off and flares alot, the female becomes engorged with eggs, shows mating stripes, poses for the male ect ect...
Finally the two are put together... It can be a very rough courtship for either or both, a fairly docile female may totally shred a males fins if left together overnight as revenge for the days overtures.
OK, my fingers are getting tired of typing and you probably know the rest