This is related to my post in the UDT forums - UDT not working on Nexus FEX units
Currently Cisco Nexus FEX layer 2 access ports are not populating the vmMembershipSummaryTable because the port ifindex is above the limit of 2048. Because the vmMembershipSummaryTable is not populated, UDT does not know which vlans to grab when it polls the dot1DBasePortTable@vlanXXX and dot1dTpFdbTable@vlanXXX. As a side note, Switch Port Mapper in the Engineer's Toolset is able to grab the MACs and map the IPs.
We need UDT to be able to poll our Nexus FEX ports and display MAC and IP info for them.