Well I did try this in Control Panel ยป Database Tools+SQL Command:
SELECT * FROM `ubbt_USER_PROFILE` WHERE `USER_ACCEPT_ADMIN_EMAILS` = "on"
But I found that the field is populated with on,off,yes, and null.
I don't quite understand why I would have four values for a field that should be just on or off
So Rick will need to respond on what the values should be.
But I believe the email tool was designed to just send email to members that have accepted admin emails.