I am wondering if the damage reduction/— granted by a Binder's Pact Augmentation class feature stacks with the Vestige's Arete damage reduction/—.
Damage Reduction: Your body becomes unnaturally tough as you gain damage reduction 5/—.
Pact Augmentation (Su): Beginning at 2nd level, you can draw additional power from the vestiges you bind. As long as you are bound to at least one vestige, you can choose one ability from the following list. Each time you rebind a vestige, you also reselect your pact augmentation ability.
As you attain higher levels, you can make additional selections from the list. You gain one additional ability at 5th, 10th, 16th, and 20th level (to a maximum of five selections at 20th level). You can choose a single ability multiple times, and their effects stack. For instance, at 16th level you could choose bonus hit points twice and damage reduction twice, gaining +10 hit points and damage reduction 2/—.