We had a park that seemingly just became EX raid eligible. Articuno day triggered two EX raids there out of the five gyms that are in the park. So I'd say yes, it can trigger an EX raid. Not sure if there's someone for whom that was their only raid at that gym, but we're pretty stoked about a new local site for EX raids.
GamePress
Zapdos day raids count toward EX passes?
Will Zapdos-raids done in EX elegible gyms grant an EX pass? Does anyone know if this happened with Articuno?
Just want to know if I should hit the EX gyms during the 3 hours since they are not in my vecinity.