Rehgar gets a stack from Pit Fighter (20) when near friendly Deathwing, even though Deathwing’s trait says he ignores friendly effects. That trait should apply to all friendly effects, even ones which don’t benefit Deathwing himself.
For the direct comparison look at Tassadar Khala’s Gift (20), which does not benefit from Deathwing. Also see Kharazim’s Radiant Dash: he can Q on any enemy hero and any friendly hero except Deathwing.