I think your question is reasonable, but as a 20+ year Delta pilot, perhaps difficult to answer without offending someone. I'll try, and apologize in advance, if someone takes offense.

Personally, I could care less whether someone applying for a job at Delta is an ALPA member or not. I'll even go a step further. Our current contract was negotiated in a hurry and there were a number of items that seemed to be thrown to the wayside. Many Delta pilots (and I'm in that group) were annoyed that DALPA spent any time negotiating for a percentage of new hires from ALPA represented carriers. I want the best people... period.

Years ago I interviewed at American and I remember during the interview a retired American pilot said "We're not hiring pilots, we're hiring Captains". I would say Delta has the same philosophy.

It's not all about stick and rudder skills, though that does (and should) factor in. Delta views its pilots as part of the brand. They want their pilots to "lead by example". They want them to follow the rules, but when it comes to customer service, they want people who take the initiative to do the right thing for the customer. That may mean going onto the ramp and getting a stroller or pushing a wheelchair, or any number of other things which are never spelled out. You must seize the moment and step up.

One of the things Delta has over the years done a really good job at is recruiting and hiring pilots. The vast, vast majority (well over 99%) are genuinely great people to fly with. They are very competent aviators, but they are great people as well. That's saying a lot, and to me it says their system works as it is.