I mean, it's not only wise advice like "do not go 35 meters if you are licenced for 30 meters" it's really that you risk to die or serious illness. As for the DAN, it works like an insurance, so I am not sure they will pay the expenses if you take unnecessary risks.
DAN DAN World : Frequently Asked Questions
Here they speak about scientists, but I think there must be a similar limitation if you are a recreational diver. What if you are OW and have an accident well below the limit of 18 meters, let's say at 50m, would they pay? I don't think so