A huge problem with Cisco's SNMP implementation on ASAs is that there is a great deal of data that has not been implemented in the SNMP agent despite being defined.
Looking at my ASA running 9.2(3)4, the only useful OID I can find regarding this is 188.8.131.52.184.108.40.206.3220.127.116.11 (crasMaxSessionsSupportable).
There is a ciscoLicenseMIB defined at OID 18.104.22.168.22.214.171.124.359, but Cisco's own SNMP object navigator reports that there are no supporting images.
Wow, going to use basically the same answer twice in one day, and the answer is based off something I just did the other day! I actually had this problem the other day where I wanted to create a report to find out the licensing on a bunch of 2911's, I tried figuring out how to do a UnDP to do it, but it didn't really get me what I wanted.
So, I did figure out that if I wanted to execute the "show license" command on all my 2900's, I could to it in the "Configs" / "Config Management" screen by doing an "Execute Script". Now, on my 2900's the "show license" command actually worked, but on the ASA's I have access to, this command doesn't exist. So, either your running a newer OS than us (definitely possible!) or your actually looking to do a "show activation-key". You could just use that command, or if you just wanted the "Total VPN Peers", you could use the command "show activation-key | i Total VPN Peers", it really depends on what you want.
Once you've done that, all your output is stored in the database from the "Transfer" queue, so don't empty it out by clearing complete jobs or anything till you get your output. To get your output, either use SQL or SWQL, I'll do it with SWQL below.
SELECT NT.NodeProperties.Nodes.IPAddress, NT.NodeProperties.Nodes.SysName, NT.NodeProperties.Nodes.MachineType, NT.DeviceOutput
FROM NCM.TransferResults NT
WHERE (RequestedScript LIKE 'show activation-key%')
This will output everything into a excel-like table in SWQL Studio that you can export to CSV and then into Excel. You can clean it up first with a text editor like VI and use excel or something to put it in a format you like.