Not at all Joel,
I take no offence at your questioning what the haze is, as I am still trying to figure it out myself and and am quite curious. Discussing it can help clarify what it could or could not be, and I don't mind at all.
The image you linked to is imaged using a lot older Canon than the 6D, and it was imaged at 400 ISO, as opposed to my Takahashi image with the modded 6D at 1600 ISO. (edit: my error, not an older Canon but a new Nikon, but still at only 400 ISO) Those factors together are going to make a huge difference in what the respective images can show, even if that one was from a darker site than mine. And then there is processing. This is an HDR image, processed carefully in Pixinsight, as well as my admittedly limited abilities allow. 
So I think it is hard to compare the two. Though here is a link comparing the two cameras that I just found. I'm happy we have 6Ds.
http://www.exploringexposure.com/blog/2014/8/28/canon-6d-vs-nikon-d600-high-iso-night-photography
To me the haze seems to be the very same shade of blue as you can see concentrated on the bottom of the Omega nebula. This is the strongest evidence to me that it is a fainter layer of the same stuff..whatever that is!
And there just should not be any gradient in this image, as it was taken from a dark site, with a Tak, and flats were used. All of those together lead me to believe that it is not a processing artifact or gradient. If not sooner, the mystery will be solved within about a year. I am retiring in a week, and will soon be putting ridiculous amounts of time on targets, including this one. Whatever it is or is not will be shown eventually!
Dean