I am not a lawyer, but my understanding is that you don't actually need to do that to be legal. You just have to clean room reverse engineer the DRM. After that, anything you have legal access to, you can legally use.
You could just get past the DRM on the BluRay drive or SD card slot or whatever, and then assuming you have legal rights to use it, load up a full set of Unreal/Unity/Renderware/whatever middleware you want and be off to the races.
Again: This caselaw pre-dates always-on-DRM and Apple-angry-tantrum-responses stuff. So this stuff was 100% legal and clear in the PS2 / Xbox / GameCube days, when there was a clear separation between the two. Now that Apple has tried to muddy the water by pretending their DRM is a "platform" that "provides value", I suspect it will be easier to confuse folks