Found these entries over and over in my vmkernal.log. VLAN20 is used for vMotion on all hosts. Investigating this now.
2016-11-16T18:18:09.266Z cpu7:11087552)NetHealthcheck: L2EchoSendVlan:1358: Build and send ticket 10829169, VLAN 20, seq 10829167 echo Eth pkt failed.
2016-11-16T18:18:09.266Z cpu7:11087552)NetHealthcheck: L2EchoTicketSend:1446: Eth send seq error: Not found
2016-11-16T18:18:09.267Z cpu10:11087553)NetHealthcheck: L2EchoSendVlan:1358: Build and send ticket 10829170, VLAN 20, seq 10829168 echo Eth pkt failed.
2016-11-16T18:18:09.267Z cpu10:11087553)NetHealthcheck: L2EchoTicketSend:1446: Eth send seq error: Not found
2016-11-16T18:18:09.267Z cpu6:11087554)NetHealthcheck: L2EchoSendVlan:1358: Build and send ticket 10829171, VLAN 20, seq 10829169 echo Eth pkt failed.
2016-11-16T18:18:09.267Z cpu6:11087554)NetHealthcheck: L2EchoTicketSend:1446: Eth send seq error: Not found
2016-11-16T18:18:09.267Z cpu10:11087555)NetHealthcheck: L2EchoSendVlan:1358: Build and send ticket 10829172, VLAN 20, seq 10829170 echo Eth pkt failed.
2016-11-16T18:18:09.267Z cpu10:11087555)NetHealthcheck: L2EchoTicketSend:1446: Eth send seq error: Not found
2016-11-16T18:18:09.267Z cpu12:11087556)NetHealthcheck: L2EchoSendVlan:1358: Build and send ticket 10829173, VLAN 20, seq 10829171 echo Eth pkt failed.
2016-11-16T18:18:09.267Z cpu12:11087556)NetHealthcheck: L2EchoTicketSend:1446: Eth send seq error: Not found
2016-11-16T18:18:09.267Z cpu5:11087557)NetHealthcheck: L2EchoSendVlan:1358: Build and send ticket 10829174, VLAN 20, seq 10829172 echo Eth pkt failed.
EDIT: Turns out the problem was the 'Teaming and Failover' Health service check on my vDS' that was causing the issue. Once I disabled that the CPU usage returned to normal. This is apparently a known issue.