Hi, rlagrange.
I don't understand your statement, "I don't think so."
If your HDMI monitor is "going to sleep", then the screen is, by definition, "dark". ("Dark" doesn't mean dim. "Dark" means there's no image on the screen.)
My DVI-connected monitor also "goes to sleep" -- the power button turns yellow, but the screen is dark. The image is sent instead to the HD TV connected via HDMI.
It still appears to me, after reading your messages (and many others in this forum), that the problem we are talking about is the image going to the wrong monitor. In your case, the image should go to the HDMI-connected monitor, but it's being sent to the VGA-connected monitor. In my case, the image should go to the DVI-connected monitor, but it's being sent to the HDMI-connected monitor.
regards, Andy_A