Yes, they seriously can. I am not surprised by anything GPC's admissions department does.
I have a Bachelor's from Vanderbilt and a Master's from Georgia Tech, both in Electrical Engineering, both with not-terrible gpa's, and GPC made me take the Compass in reading and writing! Because Vanderbilt had a fairly flexible liberal arts core for engineers, I never had to take a class from the English department. Because GPC does not teach classics or archaeology or much in the way of engineering, and because they only transfer courses that they teach that are relevant to your proposed major, and because they only transfer freshman and sophomore level classes, they only allowed 15 of my college credits to transfer. So they admitted me as a FRESHMAN. And required a transcript from my high school.
Some of my credits I have gotten them to accept on petition, since they are the same content as GPC courses but with different names.
If they have accepted transfer credits in English and Math, you should have a case for exempting the Compass Test. Which sections are they requiring?
If you send them your SAT scores and they are high enough (they don't have to be very high), that is another way of exempting the Compass.