Checking and deployment are necessary concerns, but not specific to Nanoc, as they can be used for static sites generated in any way (not just Nanoc).
Extracting a generic checking system or deployment system out of Nanoc might be useful in making Nanoc more focused, and allow it to be reused in other places.
Reasons for not doing it:
Is it worth it? What do I gain from it?
Does extracting checking+deploying into separate solutions mean more maintenance overhead? How will I support this? Or, if I won’t support it, why do it at all?