You could test by checking parity between the count of enemy animation sprites and enemy hitbox sprites, if there is a difference, test each for overlapping and if the hitbox is not overlapping an animation sprite at the same location , spawn one.
Or just spawn/pin each time an enemy is created in a single event.
It's still a little messy keeping track of things - I have some pinned stuff for debugging purposes in a game I'm working on and have to check the pin status of the animation sprites, and destroy them if the object they were pinned to was destroyed.
Hopefully there'll be support soon with spriter integration for a generic hitbox for a character sprite.