How can I monitor VNC via Nagios?

I have a number of remote sites which have VNC running on a few computers for support purposes. They are (obviously) only available on our internal network.

I am using Nagios to keep track of all the systems in the network and I want to have it check to make sure the VNC server is running on the appropriate hosts.

There is a 'check_vnc' plugin available here but it relies on VNC Snapshot which I don't want to use. Certainly I could use it, but it adds more complexity and dependency, which I want to avoid.

It seems simpler to just use check_tcp to make sure I get the proper response to a connection request for VNC, e.g. port 5900, send a connect string, get back framebuffer info. My real question, I suppose, is this: What is the 'proper' generic connect string for VNC (I use both UltraVNC and RealVNC) and what is the expected response?

If it's really easier to use the VNC Snapshot and check_vnc, let me know. I just can't imagine that a string of text isn't easier, faster, and less bandwidth intensive to monitor.

This should work for vnc:

check_tcp -H $HOSTADDRESS$ -p 5900 -w 5 -c 8 -e "RFB"