I do it, but APPERENTLY the community frowns upon such behavior.
if you do, you need to be VERY sure the female is a seasoned mater. If not, she'll only aggitate the male. I would reccomend breeding the pair quite frequently before you do this. After though, I don't really see an issue with it. Males are very tolerant of females who resemble those they've mated with frequently.
Edit: If you do however just plop them in there make sure you have objects the females can swim around and through. PLenty of objects to slow down an overly agressive male, plants decorations etc etc. Males are pretty fast swimmers in a straight line, but that long finnage makes it much harder to manuver at quicker speeds. I would reccommend a five gallon tank for two fish. Enough space for personal room and yet close enough that they can always be in sight of one another. Initally when they forget about the other betta fish it just triggers the same agressive response the next time they come into sight of the other fish.
I'd say a fair amount of plant matter and decorations, but enough free swimming room at the surface for interaction.