I'm just returning from vacation, but it didn't look like you received an
answer on ADSM support of MS-Exchange, so I hope I'm not too late!

ADSM can do an offline backup of MS-Exchange using ADSM commands directly.
Online backups are provided through NT, but they do not suport the X/open
api so the data cannot be sent directly to ADSM.  Also, unfortunately,
the NT backup utility does not provide an option to back up to a file, so
you can't do an online backup to a file, and then back up that file with
ADSM.

However, a customer in NYC does have an updated version of backup exec
from Seagate that does allow backup to a file, and then they are using ADSM
to back up the file.  The contact in seagate I've spoken with says this
backup exec enhancement is not part of the GA product, and only two or three
customers have it.  Here is a seagate contact if you want to follow up
on this for your shop: Deborah Noble, dnoble AT smg.seagate DOT com.  
407-333-7714.
I don't know what if they will offer this to other customers.

In the meantime, ADSM development is working with Microsoft to provide
a better solution for MS-Exchange.  No details can be provided at this time.
Thanks,
Cyndie Behrens
IBM - San Jose
408-927-3627
cbehrens AT vnet.ibm DOT com