See my post here regarding how to use mhvtl with iSCSI:
viewtopic.php?f=23&t=32
See these screen shots as an indication of a working operation.
Microsoft iSCSI Inititator connected:

MHVTL Medium Changer and 4 DLT tape drives recognized and configured in Windows Device Manager:

Tape drives using Symantec drivers updated by Backup Exec during installation:

MHVTL Medium Changer and Drives in use in Backup Exec:

MHVTL Media:

Successful Backup Job:

Detail of Successful Backup Job:

Detail of Successful Restore:
