I won't pretend to understand the exact business model, but it sounds like this is an entirely different can of worms. Unless there is a lot more clarification, I don't see why this is an issue, though.

The few people I know who have photographed a concert in some professional capacity have done so for someone else on a paid contract. Usually the performer or the venue... it's kind of like a wedding photographer in that sense (in my mind, at least) and I'd be appalled if a wedding photographer started making a fuss because he doesn't own the rights to the pictures.

Of course, if Swift (or the venue) is not paying the photographers (and she isn't), then clearly there must be some financial motivation for them to go do this anyways, at which point you gotta weigh the pros and cons of taking pictures you won't own the rights to...

I'd be surprised—I'm pretty sure the photographer does own the rights to photos they took, unless he/she explicitly signs them away, so there's nothing to fuss about.

That said, I'd expect to be thrown out more often than not if I started showing up to random weddings as an uninvited photographer. No one has to let me take pictures in their private space, but they might do so with terms attached.