I don't have the GMC bike rack, but I have friends who have a similar hitch-mounted rack. This type of rack works well, but - although the rack tilts down a bit to allow the hatch door to open - the rack will still be in the way when loading large gear items.
I would highly recommend the Yakima "Swing Daddy," which I purchased shortly after buying my Acadia. This rack holds up to four bikes, can take a ski/snowboard accessory rack (sold separately), and can smoothly swing - fully loaded - completely to the side of the vehicle. This swing feature is excellent because it allows complete access to the back of the Acadia.
The Yakima Swing Daddy fits perfectly in the Acadia's hitch. A couple of things to note: (1) the sonar park assist will beep several times and then turn itself off (the park assist assumes there is an object in the way, which there is), and (2) the backup camera is somewhat obscured (I've tried it with one bike; there's still a good camera view through the bike).
For easy on/off installation, I bought a separate socket wrench and socket that I keep with the rack (the rack comes with a wrench, but the socket wrench works much faster).
At a list price of $460, it's higher than the GMC model, but online stores such as Amazon sell the Swing Daddy for as low as $368.
The rack you bought looks good and the price is right. Four guys and their bikes sounds like a fun trip in an Acadia. The Yakima Swing Daddy is a very beefy rack, but I haven't tried it with four bikes yet. I did find that I frequently used the swing feature to get full access to the back of the vehicle (remove one pin and turn a handle a few revolutions to release and swing the rack to the side of the vehicle). 8)
We just got back an the rack was AWESOME!! It loaded up quickly and when we needed to load and unload the swing down feature worked great allowing easy access to the rear without removing the bikes. The rack was quiet as a mouse. No regrets getting this one!!