Cisco devices that support SNMPv3 are all tri-lingual. LMS, on the other hand, will opt to use SNMPv3 if it is configured. If SNMPv3 fails, LMS apps will NOT fallback to v1/v2c. However, if you choose not to configure SNMPv3 credentials in LMS for a specific device, LMS apps will use the v1/v2c credentials that you configure instead.