No.
You can think of it as that the monster needs to be 'suffused' with the property of the thing behind the DR slash.
Evil monsters that have DR x/good are not inherently good, thus cannot penetrate DR x/good. If they have the evil subtype (most monster with DR x/good have) they are so suffused with evil that their natural weapons count as evil.
Monsters with DR x/magic are so suffused with magic that they can penetrate DR x/magic (make sense?)
Monsters with DR x/epic are so 'epic' that their attacks can penetrate DR x/epic.
But (obviously) a golem with DR x/adamantine is rarely ever 'really adamantine', nor is a werewolf made of silver, nor do fey with DR x/cold iron have the metal running through their veins.
Creatures with DR x/material are rarely 'suffused' with that material, usually it's even antithetical to them.
The 3.5 way of treating DR actually makes sense....