It's always someone processing the very flight (flight manager) who's making the decision, that's the nature of "stand-by". Generic CI or lounge staff can't do it.

However, the CI or lounge staff at an LH hub can always call someone the gate, so your UPG can be confirmed right away and you can proceed to the FCL. That's what happened in 100% of the cases I used a paper SWU at MUC (as long as there were any free seats available, of course).

At remote stations, the FM or station manager is usually present at CI and helping out, anyway, so they usually don't even have to make a call.

In any case, the stand-by UPG is confirmed based on physical seat availability (again, that's the nature of "stand-by"). As long as seats are available (meaning the regular UPG list has been cleared and they don't expect any additional pax rerouted from other flights or any last minute full-fare buyers), they'll accept the stand-by SWU right away. Hey, it's money (kind of) and at this time, those seats have a very limited expiration date, so better move the 1K waving a SWU into F than opup the HON sitting in oversold C.

Personally, when I used to be a SEN waving an SWU, I never had any problems. Even when my desired COS was sold out, they always held me on their number one UPG spot until the last minute, just in case there'd be a no-show.