yes, it is possible since the different brightness of regions of sky aren't inside flat information. Before I use skyglow filter my photos always have a side more dark than the other. Different from vignetting, that has the center of image more bright.
At that time, many people told me: "make more flats, you need dozens of flats, make new flats ..." ... for what ? I tried to do a "flat" for my sky glow, and it was a disastre ! Solution, only with filter .
