Dear MZIK,
We are using CSC SSM with ISA 2000 we ara not facing any issues its working fine.
while you can use it directly you dont need any proxy server CSC can provide you detail filtering and url blocking.
you can use with AD you can use AD group to define exception.
CSC can show you the proper blocking message or you can define your own.its good device.
If you need any help you can contact me.
Regards,
Azhar