As others have said, that depends somewhat on the type of campaign.
Dungeon crawling where each enemy will likely only face you once or twice in a relatively short period? Yeah, that DR is practically DR/-; most beings capable of bypassing it will likely do so easily for other forms as well.
A campaign with frequently recurring enemies and/or forces of enemies? Yeah, expect a Cloud of Knives to the face by round 3 at the latest.