If by "managed DR," you mean you've contracted with an IT recovery services vendor to host your recovery solution. You either "rent" their hardware or you pay $$ per square foot to place your hardware on their floor. Either way, there are only two items of primary importance you want to see, they are both the result of your regular recovery plan exercises:
1. Did executing the plan deliver system availability to users within the RTO?
2. Did executing the plan deliver the data without loss exceeding the RPO?
You see, When you've done your business impact analysis (BIA, you have established the RTO and RPO for every system. From that, strategies to meet the RTO's and RPO's were selected. Then, plans were written to implement those strategies, meaning, all the necessary arrangements and resources, including assigned recovery staff, hardware, networks, application source code, back-up data (whether on tape, streamed, or both), licenses/keys, etc., are made available to support the recovery.
So, when you "test," you should be seeing recovery staff following the plans to a successful recovery within RTO's and RPO's. Sure, it's a simple thing, but I can't tell you how many clients and companies I've seen that simply line everything up, and go through the motions of recovery without taking into account the difference between that and what a "real" disaster is like, when half the staff can't respond because roads and/or bridges are out, or the data center , where they are running the exercise scenario, is on fire. Does the plan address that? How would they exercise that scenario? They don't. Are they vulnerable, absolutely.
Hope this helps.