Net::SNMP doesn't depend on any SNMP libraries other than itself; it's a full implementation of SNMP. Clearly it can't be a replacement for SNMP, because SNMP is a protocol, while Net::SNMP is a Perl module. Whether or not there is an snmpd process running doesn't have anything to do with either the presence of SNMP libraries or Net::SNMP. Finally, if Net::SNMP (or nearly any Perl module) is missing one of its dependencies, it won't fail silently; it will raise an exception.