No, they don't. They make you show that you have a beacon, shovel, probe, and climbing skins to purchase a backcountry lift pass. It's simply a filter to prevent people from abusing the discounted lift ticket.

I estimate that roughly half of the people in the W-B slack/back-country on any given day have purchased a backcountry pass. The rest are season pass holders who would never be questioned by anyone about what gear they have with them. As someone mentioned above, it is unlikely that any ski resort would take on the liability of "approving" that anyone accessing the backcountry from within their boundary was suitably prepared to do so.

The backcountry "gates" at W-B are purely cosmetic. They serve no enforcement function and there certainly is no requirement that you pass through them to access the backcountry. At best they are a place to hang a few warning signs that may, or may not, be read by those who pass by them. I think they do make an effort to post the latest avy bulletin, which is convenient if you don't want to go into one of the lodges. The gate on Blackcomb glacier does have a beacon check device, which is also convenient.