Yes for the immigration listing, which accepts a provincial licence. The U.S. hospital will still normally require its own state licence before she practises, and the health care worker certificate is required for admission regardless of which licence the letter cites.
Three documents, three different owners
The listing for Registered Nurse permits a state or provincial licence or a Licenciatura Degree, so a nurse registered in Saskatchewan meets the qualification rule on paper. The difficulty is that three different bodies control the timing. The provincial regulator controls the licence she already holds.
The U.S. state board controls the licence her employer wants her to have before her first shift, and boards vary widely in how long endorsement or examination takes. An approved certifying organization controls the health care worker certificate, which the port-of-entry officer will ask for and which cannot be waived by the hospital.
Map those three timelines before accepting a start date. A nurse who arrives with a valid TN letter but no certificate is refused admission, and one who arrives with everything but no state licence may be admitted and then unable to work. Neither outcome is the officer's fault.
Hypothetical example: An operating-room nurse accepts a position in a small surgical centre and has Saskatchewan registration but no issued licence from the destination state. The first review should produce a date chart for the registration, the health care worker certificate and the employer's intended first shift. The state-board correspondence settles whether the offered start date is realistic; it does not change the immigration qualification.
If the certificate expires before travel, or the letter names a credential not yet issued, postpone the application and correct the document set rather than hoping an oral explanation will cure the mismatch.