Unfortunately questions related to Azure DevOps is out of scope for this forum. At this time you'll need to continue to post over on the forums that Azure DevOps does support on Stack Overflow.
In terms of your actual question I believe you should be fine provided the contractor logs into VS using their email address and that email address is tied to their VS Enterprise license AND you have allowed external users to connect to your Azure DevOps instance AND you add their email address to your list of users. That's how I have historically done it without any issues. But even then I used my company email in Azure DevOps, my personal email for VS Enterprise and just ensured that when I connected to DevOps I used my company email credentials. But that was a couple of years ago.