I feel like it's better to embed the tool in a language, or many community supported languages than embed a programming language in the tool.
The entire script is executed atomically, with no other administrative operations taking effect concurrently.
If a fatal error is returned, the channel program may have not executed at all, may have partially executed, or may have fully executed but failed to pass a return value back to userland.
That's the whole point, as I understand it. The channel programs are executed in the kernel, in a way that cannot be done by external programs. Some more details here[1].
edit: I also think you should have included the note, which says
Note: ZFS API functions do not generate Fatal Errors when correctly invoked, they return an error code and the channel program continues executing.
So while it's not quite ACID-level, its not as bad as it sounds without that note.