Hi Geoff,
One of my machines is configured exactly the same way except for the TSM
part(in the works.)  We have recently installed a large EMC backend for our
Solaris and NT machines.  I've been asked the same question as you.  Here is
what I found out.  Yes you can backup over a SAN.

BUT it currently only works with certain agents.  From what I was told you
can use the Oracle, Exchange and SQL agents.  Currently the normal
backup/archive client software does not support SAN backups but is in the
works.