I've used instructions similar to those to get AMT KVM working with a normal VNC client, it works fine. The only catch is that the AMT seems to intercept all traffic to port 5900 coming in through the NIC, not just that addressed to the IP of the AMT. It's only the "legacy" port 5900 VNC which is affected, the other ports such as 16992 for AMT's web admin are unaffected.