yes you can.. all the different tail types are one species betta spendens. its like dogs.. they all look different but they are all the same species, just different breeds
What would be more dominant ??
Will it have traits of both fish or just one?
It's generally not recommended to mix tail types unless you have a specific goal in mind. Crowntails have been bred for years to show the best crowntail characteristics, HMs have been bred to show the best HM characteristics, etc. and mixing them just creates a mess more often than not. But any different tail types will breed with each other just fine, and there are even a few other species that will hybridize with splendens and produce fertile offspring.