No and no. Mistral and StackStorm actions are not interchangeable.
The major thing that is the same between Mistral in OpenStack and in StackStorm is the Mistral workflow language (and the system service processing that language).
When learning workflows in StackStorm, I recommend you look at and use Orquesta instead of Mistral. The workflow language is similar to Mistral, but makes it significantly faster since it runs directly in StackStorm. Plus, it doesn’t have Unicode issues like Mistral. It’s just all around awesome!