I've been able to pull a couple stats from a netscreen SSL VPN - Memory, CPU, and a couple others, but for some reason I cannot get the concurrent users to pull properly.
If you go in to create a custom mib (a tutorial is on packeteer web site on how to do this if you haven't done it) and go to:
1.3.6.1.4.1.12532.10 for CPU Utilization
1.3.6.1.4.1.12532.11 for Memory
but again, I cannot seem to get the concurrent users to work.