You can set up a discovery filter to limit what is discovered.
Here is a filter for all Cisco devices:
CiscoFilter "all cisco devices"
{ "SNMP sysObjectID" ~ .1.3.6.1.4.1.9.1.* }
A filter expression can be written that would allow you to also include
other network device SNMP sys object ID's such as Wellfleet,
.1.3.6.1.4.1.18.*, or Cayman, .1.3.6.1.4.1.7.2.*
See the Scalability and Distribution Guide Appendix A and remember to use
the ovfiltertest and ovfiltercheck.