It's simpler than that. I just went through a DP DR planning scenario with an HP consultant and he showed me how to get a media report just for the IDB backup - or in our case, a copy job.
Set up a report group going through "Reports on a single session", and select "Session Media report".
Then set up a Notification using that report group, tell it to run against the backup (or copy to tape) spec, at job completion, and have it email the results to you in ASCII mode.
VOILA! You know which tape your IDB backup is on. If you're worried about DR, send it to a couple of different places so that you can access the message even if your primary site goes down... then again, you ARE sending the IDB offsite somehow, right? We do ours daily.
Ken