How could I send a net-snmp GET request, such that:
netsnmp_check_vb_type
will return SNMP_ERR_WRONGTYPE?
You'd need to modify the agent you were talking to so that it would send back that error code for a GET. No agent out there should be doing that for a GET request unless there was a bug in the agent. In other words: you'd have to put a bug in the agent!
I think that's impossible, as wrong type check should only work for SET requests.