The Sierra should be a heavier frame than the Ultralites many of us have as they have twice the cargo carrying capacity. On my Rockwood, the frame isn't a true I-beam, it's welded flat stock that's 0.125" and the bumper is only 0.080".
You can check the size/thickness of the I-beam, gauge of the bumper and the quality/quantity of weld holding it to the frame rails and let that be your judge.
I've had a 2 bike rack on the back of ours for 3 years and haven't had an issue, but your results may vary!
Nights camped in 2013 - 55, 2014 - 105, 2015 - 63