The issue here is "if" you have engine problems within the warranty period. In that case, it would become the responsibility of the owner, who choose to either DIY, or go to a non MB dealer, to show through the documentation, that you fulfilled the requirements under MB's warranty. If you cannot demonstrate through the record, that you used the recommended oils, they may, and can deny coverage for the nesessary repair. It is truely is that simple.
I had that exact same issue with a VW I owned. They were physically stunned (jaw dropped) when I produced my oil change records showing the "exact" oil VW called for. Vehicle was three weeks in the shop, for a major engine failure/rebuild. Covered in full. The service writer actually said "the've never seen a customer, at their dealership, produce records for every oil change within the mileage requirement before" They also said they would have denied warranty coverage, if not for the records. So IMHO, if you do not follow MB's specs to the letter, you might be in for an unnessary fight.