I found a resolution on my own, see:
I received the "fit-Headless" display (monitor) emulator today; with it, I am able to ping and SSH just fine into the Intel NUC running Ubuntu ver. 14.10 server, without a monitor and without a keyboard connected. I guess the keyboard is not required, just the monitor or the emulator is needed. 1920 x 1080 resolution is the max if I wanted to remote in with GUI like with VNC, and the fit-Headless was just $15 on Amazon with no need for a huge monitor on a rack shelf.
A friend of mine suggested I could have modified GRUB, but I didn't know what options to modify in GRUB...
Fit PC also has another HDMI adapter that can emulate up to 2880 x 1800 screen resolution and makes the Intel NUC think there is a monitor connected, it is called "fit-Headless 4K" and it usually costs about $40.
I hope this helps someone else with the same issue...
Thanks a lot for sharing this information with us and other users.