Running fastboot DOES produce the identifier token BUT
Plugging it into HTC's site produces the following error:
We're sorry, but it appears your attempt to unlock the bootloader on this device has failed. This could be caused by several factors including simple errors in the entry of the unlock token, problems with your device, or a lack of manufacturer support for the unlocking process. Please see the specific error code listed below, and try again if necessary.
Error Code: 160.
Error Reason: MID Not Allowed
I'm guessing the Verizon M8 has some extra level of protection (or those SN's are premarked for exclusion).