What messages are you getting back from the agent?
I presume that they are about the Interfaces on the router / switch.
If so, then this is the IP / Mib2 policy that is doing this.
I don't have a working TNG system in fromt of me so I'm afraid I may not be 100% accurate, sorry.
basically, it will always do this unless you specifically tell the DSM not to.
You can either - edit the ip.atp file (NSM) and comment out the entries to Cisco.
Or run dsmwiz and tell it that the IP agent cannot be found in the Cisco class.
Either way - run resetdsm afterwards.
This is all a bit vague, so you may need to play around a bit to get it working. Next time I am at a working system i will have a look.
However, if you do this then the cisco objects will basically do nothing at all and have no useful purpose.
I would personnaly keep the DSM monitoring going and just mask the messages out at the console level.
This way you can choose to act on certain messages in the future without having to re-configure the DSM - if for instance you wanted to monitor a particular interface or port.