Did you update to ESXi 5.1 Update 1, and install the associated version of the VMware Tools (version 9.0.5) on your VMs? This is suppose to resolve the issue.
Assuming so, deleting the unity.dll resolves a separate warning message seen whenever someone logs into the VM via RDP:
[ warning] [vmusr:vmtoolsd] Failed registration of app type 2 (Signals) from plugin unity.
The tools.conf should be sufficient to resolve the RDP errors if the file is saved to the correct location and has the correct parameters.
Finally, note that the KB says "If there are users logged in to more than one session, restarting the VMTools service may not be sufficient. You may have to kill the vmtoolsd.exe process for all instances."
All of that fails, you can:
1. Open a ticket with VMware Support
2. Modify the tools.conf file to log the errors/warnings to a log file, and therefore at least remove the spew from the Event Viewer. For guidance on how to redirect the VMware Tool log messages to a file and setup rotations so the log doesn't fill up the drive: http://kb.vmware.com/kb/1007873
Hope this helps!