Sure, but there's a time and a place. Outages involve high tensions and fog of war; and you said it yourself, you're already ready to blame them for not having backup generators in this hypothetical example. The midst of an outage is not the time to start casting blame, on people, organizations, processes, providers, whatever. Outages are the time to fix; retros are the time to blame (within productive reason, of course).
I would still blame them for not having back up generators though.
However a failure to plan for emergencies is different from other kinds of failure.