Unfortunately, there is no way to tell for sure if a waitlist RUC is correctly applied. The only way to tell is when the RUC actually clears and your flight is booked as RP class.

While the RUC process is almost entirely opaque, there are a couple of "hints" of a correctly applied waitlist.

1) When viewing a waitlisted segment on the DL.com web site (not the app), there will be two seat maps for the same flight. The first seat map shows the coach seat you are currently in, and the second seat map for the same flight says "you may not select seats for this flight" or something like that. This second seat map corresponds to a part of the waitlist process, and indicates that at least one step of the multi-step process to add an RUC waitlist was actually done. Unfortunately, this does NOT indicate that the other manual steps of the RUC waitlist process were successfully completed by the agent.

2) Assuming the waitlist does not clear prior to check-in, the second hint is the upgrade waitlist. If the RUC waitlist request was coded correctly, you should show up at or very near the top of the upgrade waitlist that you can see on DL.com or the app. If you find yourself at your "usual" spot on the upgrade waitlist, this is a clue that the RUC waitlist request was not coded correctly.

3) The RUC is a form of "payment". Until the RUC clears, it remains "unused" so a waitlisted RUC will still show in your wallet as "open".