There
Uber is usually easier before the show because demand is spread out.
Red Rocks feeder page
Uber after Red Rocks: possible, but not the best default
Direct answer
Uber after Red Rocks is possible, but it is not the most reliable default after a sold-out show. If you want the ride home settled before the encore, choose a shuttle.
Back
After the show, the pickup zone, traffic pattern, wait time, and surge pricing all work against you.
Better move
Use a shuttle if you do not want to leave early or gamble on the post-show pickup.
Recommendation
Do not make Uber the plan unless you are comfortable waiting, paying surge, or leaving early. For most visitors, shuttle is the cleaner Red Rocks return plan.