Well, it's not EI metal; it's ASL metal being wet leased to EI. But that's in the range of eligible EI flight numbers shown here, so things should be fine--this shouldn't be any different than earning miles on an EI turboprop flight operated by Stobart Air or, before that partnership ended, a DL flight operated by SkyWest or Compass. The only instance I'm aware of where AS doesn't credit miles for a regional/contractor operating for a mainline partner is BA CityFlyer.