Very unlikely. They probably account for things like absorption when calculating redshift and the corresponding numbers that they're getting from their measurem

Very unlikely. They probably account for things like absorption when calculating redshift and the corresponding numbers that they're getting from their measurements. For instance, each star/galaxy has a spectral composition that can indicate what it's made of. This can be correlated with brightness for other stars and can be determined how bright it should be. Redshift would shift the entire spectral composition towards the red, while absorption would remove certain bands. There's probably many other ways they've verified redshift too that I'm not thinking of.