Comment by andrewflnr

There's already a ton of redshift from the universe expanding, so they're definitely correcting their spectra for some amount of redshift. I'd love to know if there's a way to tell the two sources of redshift apart, or if significant redshift from climbing away from the hole just makes it look a smidge farther away.

But honestly I'd guess that the light is emitted too far from the horizon to be redshifted very much by the black hole.