System-based SNMP started with V4, if memory serves me correctly.
Deactivated by Default, you must first enable SNMP via "Application Control" in Assistant. (You will need to click around Assistant and locate "Application Control". I think it resides in V4 or V5 "Unix Base Admin", but I just do not recall. In V6, it is found under a different folder in Assistant). After enabling SNMP, wait for the response that it has been successfully enabled, then either logoff from Assistant, then login again, or simply wait 30 seconds and reload the browser.
In Assistant -> Diagnostics, you should see a new folder named "Fault Management". Here you will see the "SNMP Configurator", which is where you configure up to 5 "traps". The MIBs may be viewed from here, but they may not save very well from here. To fetch the MIBs properly, you will need to use Expert Access file transfer to/from Unix in HiPath 4000 V4 or V5, and change directory to the "opt/ncc/mibs" folder.
In HiPath 4000 V6, you must use WinSCP tool and access Assistant virtual machine by using the IP address of Assistant. You will login using the username and password for Assistant. The MIBs will be located in the same folder as above, but this OS is Linux - not Unix. WinSCP (available via internet) simplifies the save process by supporting drag & drop.
I believe the 4K supports SNMP v1.1.
Hope this helps.