UPDATE:  This issue appears to be resolved with the newest set of VMWare Tools 8.6.5.  These tools are packaged with ESXi 5U1 which is available here:

https://my.vmware.com/web/vmware/details/esxi50u1/dHRAYndkZSpidHclZQ==#product_downloads

Investigation into this issue has revealed the following:

The nxagent server is grabbed by a vmware-tools process. Killing the grabbing process restores normal functioning of the NX session.

This would appear to be a bug in VMWare Tools 8.6.0.

Suggested workaround:
The problem occurs as vmware-user is automatically run by Gnome at startup. An alternate script could be run in order to skip vmware-user if the display number is low (nxagent is coded to use display number > 1000).

Step 1: Edit file /etc/vmware-tools/vmware-user.desktop. Replace the content with the following:

[Desktop Entry]
Type=Application
Encoding=UTF-8
# NB: Generation of the Open VM Tools tarball depends on this line. If you change it
# be sure to also fix up OVT staging targets.
Exec=/usr/bin/vmware-user-alternative.sh
Name=VMware User Agent
# KDE bug 190522: KDE does not autostart items with NoDisplay=tru...
# NoDisplay=true
X-KDE-autostart-phase=1

Step 2: Create new file /usr/bin/vmware-user-alternative.sh:

#!/bin/bash
display_number=`echo $DISPLAY | cut -d: -f 2 | cut -d. -f 1`
if test "x$display_number" = "x"; then
  display_number=0
fi
if test $display_number -lt 200 ; then
  exec /usr/bin/vmware-user "$@"
fi

Step 3: Make the script executable and suided:

# chmod 4555 /usr/bin/vmware-user-alternative.sh