In my honest opinion (not firmly held) it should remain DR, but only because I think it should be differentiated from toughness. Were I open to modifying the Toughness perk (I'm not) I would actually make Toughness DR and Barkskin DT. As you can see I am conflicted. I would love to see a logical, perhaps numerical, argument for DR/DT and what amount.
There are a fair amount of armors in TTW that are not in FNV. A lot of those had very obvious parallels that could be drawn (Talon Combat Armor is obviously repainted Combat Armor). Some weren't and we were forced to find its closes neighbor that exists in both games and extrapolate from there.
Were we to follow that pattern, then Barkskin should be +3DT because the original Toughness-Barkskin ratio was 2-1. The unpleasant problem with that line of reasoning was that Toughness has been changed from 1 rank to 2. In FO3 Barkskin was given a "rank" of half a perk. If we set Barkskin to +3 DT it becomes equal to one whole perk. If we set it to +2 it is a bit more than half a perk. +1 is a bit less than half a perk. Considering the Toughness-Barkskin ratio and the "half a perk" measure, I believe that +2DT is the best compromise and best solution.