Yes, I do use a Dexcom G5 and I do lift regularly. Unfortunately, I don't have the best of luck (or any luck) with wearing the sensor on my arm. Just as
@catapillar mentioned, the sensor wire bent the wrong way into my muscle which caused some discomfort and inaccurate readings. I wasted three sensors (not consecutively but over the course of a few months) before deciding I couldn't wear it on my arm.
I actually wear my sensor below my left arm on my rib cage. If I put my arms by my side it's right in front of my elbow joint (if that helps you visualize). That allows me to wear a 4" powerlifting weight belt without issue. It doesn't get in the way of running or hinder my range of motion. Oddly enough, it's extremely accurate there as well and it's far enough on my side that I can sleep on my stomach or back. The sensor wire also has a slight curve to it which follows the curvature of my rib cage so it's less likely to get bend the wrong way.