Distance field for foliage?

Is distance field calculated for foliage too in addition to static meshes?
A well optimized outdoor scene should contain lots of foliage (rocks, trees etc.), hence distance field would be useless if not taking into account foliage.

It should work fine, from the Docs:
"Generate Distance Field As If Two Sided on the foliage meshes"

this is way too vague to be an answer to the original question !

The distance field is global, so the amount of static distance fields shouldn’t cause any performance issues.

Make sure you check “affect distance field lighting” in the instance settings.