Well after reading so much from these forums it seems to me that sometimes is just LUCK, some people have manage to kept the 2 together with no problem, while others ended up with casualties. Same as with the male guppies some Bettas think they are bettas and bye bye guppy but in some cases they get along just fine.
If you really want to try it. Put it in the fact and put a close eye on them and see what happens any aggression and take him out. If nothing bad happens LUCKY YOU.