Have you tried checking the manual, Randy?
The man page for ADDRESS VOX SENDMAIL Rexx command does not include a BCC parameter.
I checked the AP source code that processes the VOX SENDMAIL command, as well, but there is no BCC processing.
There may be a way to setup BCC recipients in the notification manager website as policy, but my test server is down ATM, so I cannot answer this question.
HTH,
Stephen