At least for RUT950 it is possible.
If you download the standard Linux MIBs and do snmpwalk on the router you will see the address translation table at OID .188.8.131.52.184.108.40.206
This contains MAC addresses and IP for all VPN clients.
The routers own MAC addresses can be found in the ifTable at OID 220.127.116.11.18.104.22.168
The routers own IPs are found at OID .22.214.171.124.126.96.36.199.1.1
The ipRouteTable is available at OID 188.8.131.52.184.108.40.206