The reasons all depend on just how "picky" your network security officer is.
Ac97 will fail any tests of security vis-a-vis intrinsic security because of the MDAC features. The older technology just can't be patched enough to be really secure. Too much to change, too many underlying assumptions that are too easily broken on a good day.
On the other hand:
If your Ac97 is on an inTRAnet as opposed to the InTERnet, and if you have a good firewall and other layers of protection, and if the Ac97 is never exposed to the InTERnet, it should work fine.
The comment above about Ac97 over wireless COULD be a performance problem issue - I don't know. But I would NEVER EVER IN A BAZILLION YEARS run Ac97 over wireless because of the (lack of) security transmission technology for such operations.
If you are, or can borrow, a network guru, you can mitigate some of that with things like IpSec or a 3rd party VPN.