Cleave,
Yes, the MTB and BMX helmets do use Snell some. Their helmets are much more like modern off road motorcycle helmets in design and materials. Snell went through some major changes a while back following several controversies about their methodology and links to industry. The DOT and especially the European Union requirements are becoming the standard but, Snell has a lot of tests and experiments that exceed the governmental agencies. When I buy motorcycle helmets I look for both Snell and DOT certification, these satisfy the AMA for MX racing.

I am not familiar enough with Snell's bicycle helmet standards since it has been dropped by the governing bodies. Too many of the bicycle helmets sold as CPSC compliant are shoddily made to me. The old Bell ad about having a $5.00 head buy a $5.00 helmet, got a million dollar head buy a Bell (substitute your favorite helmet brand here, Bell has gone through too many owners and manufacturers for my taste, the bicycle and motorcycle divisions are supposedly different owners, I lost track.) Arai from Japan is one of the 2 manufacturers of motorcycle helmets in the high end range that exceed all standards for testing. You can easily pay $750.00 and up for their helmets.

Bill