I am having this same problem. I have tried all three VNC clients through the MDT, all show a black screen. I am able to control the mouse and type through vnc, but the screen shows black. Same disconnecting behavior as well.
Computer model: MS-7830
Product name: CSM-Q87M-E43 (MS-7830)
Vendor: American Megatrends Inc.
Release date: 04/01/2015
Family: Intel® Core™ i7 Processor
Socket: SOCKET 0
Version: Intel(R) Core(TM) i7-4790 CPU @ 3.60GHz
Intel® Active Management Technology firmware version: 9.0.30-build 1482