I did some testing with elementalist(earth) on the pgcc and found that the 5/+5 dr they get from their path feature does not stack with EDR, yet it seems like they still encourage you to take those feats ingame. I'm not sure if this is an oversight, or just the way it was intended for this class to be.
The Earth Elementalist package when making a new character states the following:
Ability Score: Constitution
Feat Recommendation: Invoker Path: Earth, Spell Focus: Evocation, Epic Damage Reduction I-III.
Specifics: This package builds into the invoker path: Earth and will recommend Earth and Acid spells. It also builds into Epic Damage Reduction and recommened Constitution instead of Charisma upon leveling up.
I've seen that EDR feats do stack in a few niche cases such as barbarian DR and EKD DR, so, I thought perhaps it applied to earth path elementalists too considering the above.
Instead, it seems you can think of the path feature as more of a free cushion during your leveling journey until your EDR overtakes it, if you still choose to take those feats. Hard to say for me if it feels very competitive over other feat options though.
To open up more unique build varieties/identities among the elementalist paths, I think the passive 5/+5 DR should stack with EDR feats if a player chooses to take them. It's already quite a heavy investment to do so over other epic feat options for a caster.