Split blades do exist, although this is the first time I've seen one on a dagger, usually I've seen them on swords. Swords of this type are assumed to be copies of Dhu-l-Faqqar, the sword of the prophet Muhammad, which was later used by his cousin Ali ibn Abi-Taaleb. The swords of this type I have seen are usually very ornate, I doubt they were ever meant for use in combat.
