If the Approvals to extend offers to each candidate workflow is enabled on the job, then it is not possible to mark a candidate as hired without first creating an offer. This is what you will see:
If the Approvals to extend offers to each candidate workflow is not enabled, then yes, it is possible to go to the Private tab on the candidate's profile page at any time and click the Mark Candidate as Hired button to indicate that a candidate has been hired. This is what you will see:
Remember that the Offer Details tab is only accessible to users who have been assigned Site Admin or Job Admin permissions along with the optional permission to see private notes, salary info, and manage offers.