If memory serves me correct. Non critical does not come to work, and they rightfully get paid for it when it's over.
Everyone on active duty is supposed to come to work, at least that's Navy policy. Can't speak for the other services. As for getting paid when it is over, yes, that's how it is supposed to work, but in cases where government shutdowns have lasted through a payday, that pay is withheld until the shutdown passes. So, although it is retroactive, technically everyone in federal uniform today is not getting paid.