Did you add your VMhost to a Windows domain?
http://www.vfrank.org/2010/09/01/esxi-4-1-ntp-active-directory/
Apparently, if the host is part of the domain it will ignore the NTP setting and sync with the PDC. My DC sync's to nist1-ny.ustiming.org and my host has apparently been getting time from my DC (they're all correct) so I haven't been able to verify this on way or the other.
