Have you tried Windows 10? I'm wondering if that would fix the problem. I considering buying one of these myself. However, I'm planning on using it headless like you. So, I'll probably hold off until I know this issue is resolved. Are you still having the issue? I'm planning on running Windows 10.
Also, are you using Remote Desktop and having the problem? I'm not planning on using Team Viewer. I want to use Remote Desktop.
From everything I've read you won't have an issue if you're using remote desktop regardless. Remote desktop doesn't use the current display's monitor like teamviewer does...
As for windows 10, i haven't tried it and i don't want to for my project. I need my NUC's to run some older software and I can't afford to have any comparability issues or bugs (It's been proven to work on windows 7).
Just give you some information.
I have used NUC5CPYH with Windows 8.1 headless with Team Viewer. Some applications did not show properly. Chrome showed white window, so you cannot use it, but IE worked fine. Sometimes, it showed black screen when starting remote to. So, It does not work with 8.1 properly.
Now, I am using it with Windows server 2012 R2. It also show white windows in some applications, but after plug in HDMI, It works fine. Black screen on team viewer appears when just turn off monitor, but wait for a few minute, screen will come back.
I have also used Windows 10, but not sure about it.
This problem can solve by plug in a HDMI to VGA adaptor. Just plug in, you do not need to really connect to a monitor. Or, wait Intel to solve it.