Reading through some online posts it seems this was a bug in MCT. When trying to make a KVM connection using the built in viewer over the redirection port it would just hang and never connect. Apparently this was fixed in the latest MCT:
Release Notes 7.0.12102.2
Resolved connection issues to KVM via the redirection port.
I'm running 7.0.12102.2 and I'm still having the same problem however. Management station is Vista SP2 (32). Remote PC HP 8200 Elite USDT running AMT 18.104.22.1689. VNC viewer on standard port works as expected.