I'd say it is acceptable. Creative, but acceptable.
While it is true that Basic Moves does not contain any such thing as Harm Yourself, and Hack and Slash explicitly talks about attacking an enemy, note that Hack and Slash also says that it applies only for a prepared enemy.
It says if you attack an enemy who is unaware of you attacking or restrained and helpless...
You just deal your damage or murder them outright, depending on the situation. Nasty stuff.
Let's see if there is a Murder Helpless Enemy move. Nope, no such thing. However, the rules explicitly say that's something you can do. Thus, concequentially, I do not see any objection to inflicting damage on yourself in the same way, e.g. by using your dagger seppuku-style or such, and apply damage on yourself right away — without subtracting armour, obviously. I'd say d4 ("bruises and scrapes at worst") would be a bit tame, but d6 would be appropriate ("spills blood").
This might even make sense lore-wise if you see it as a sacrifice which you use for "paying" for the healing.