I can only say that Friends of C&TS members who are volunteering on the property must have the photo ID, wear it, and carry an AHR-signed copy of the release form on their person. We were informed in no uncertain terms that was a requirement.
On opening day, I didn't see anyone actively checking for yard passes or asking people to leave the yard, but the railroad people absolutely had their hands full with getting the trains out and conducting some of the opening day festivities.
Your best bet is to call the C&TS and ask.