Sounds like you got one of the special Vibes with the GM spoiler package. Lucky you!
Looking at it, the bumper cover does appear to be lower than a stock bumper. One thing I know, the hitch from a 03-08 Vibe will fit a regular 09-10 Vibe, but like yours, my 10 GT has a lower bumper cover. I got an older model hitch for $50, but was able to temporarily remove the lower black plastic panel on my bumper cover to give me enough room for the hitch. I didn't want to spend $180 to buy a new one for what was probably a one time deal towing a u-haul trailer. According to discounthitches.com , a local trailer place, CURT Trailer Hitch #12221, #122211, #122212, or #122213 will fit a 2009-2010 Vibe GT and also the earlier model GTs. The counter guy could not confirm it 100%, but he did tell me if I ordered it, they would test fit it and of course if it did not work, they would take it back.
I just looked up a Matrix and for the XR and XRS, they show two options, one that requires facia cutting and one that does not require it. The part numbers I listed above are the ones that require cutting. The one that does not require cutting is CURT Trailer Hitch #12013, #120131, #120132, or #120133. Different part #s just have different ball mounts included. Sounds like the XRS hitch would be the best to try.
Hope this helps!