I've noticed that on ESXi with just a standard vswitch, in a UCSM blade running 5.5.
It appears the VMware implementation of CDP may not be polling correctly, or the GUI doesn't report correctly.
Try logging into the esxi host via SSH, and run: esxcfg-nics -l
In my lab the GUI says Full Duplex: Disabled, but output from esxcfg-nics -l says: Full in the Duplex column. Appears the GUI doesn't always agree with the CLI in ESXi. Maybe just an ESXi GUI bug.
I've also noticed that in UCSM or where QOS determines maximum MTU, that the MTU will also report 1500 from VMware, even on a vnic set to jumbo that is pinned to an uplink that allows jumbo frames (i.e. best effort class allows 9000)
Thanks,
Kirk...