Like Kissy says, you can breed most betta types together but you won't necessarily get great results in terms of finnage and colouration.
The usual reason for breeding different types is to improve upon or acheive a specific feature such as tail type or finnage.
For example, I have a HM-SD cross male betta and the result is basically a SD tail fin, maybe slightly more rounded but not as broad as a HM tail I beleive.
You will probably end up with some very pretty veiltail bettas whatever the case, good luck with it