No. IMO, no one is "Tier One" until they get the interview invitation.

Would Delta (or any airline) ever admit to interviewing/hiring anyone less than a "Tier 1" pilot?

How would that sound in an investigation? "Well, you see, the FO was a Tier Two guy, so that explains him sliding off the end of the runway." See what they did there?

The "tier" system is all games. Not sure what they're trying to achieve, but at DL, everything is intentional.