In red shift (from any of the 4 known causes), ALL the photons see their observed wavelength become longer than the wavelength at which they were emitted.
For example, there is a bunch of gaps in the spectrum of light that goes through the hydrogen "atmosphere" of a star. These gaps are always caused at the same wavelengths. Always.
When the light undergoes redshift, the wavelengths at which the gaps are observed are ALL longer than whatever they were at emission. The pattern of the gaps retains the same shape (making the pattern recognized as the "hydrogen forest" because it looked like a clump of trees in the old-type spectrum graphs)
When the light undergoes only attenuation, the gaps remain at the same wavelengths. It is the quantity of light that gets reduced.
A star that is observed through a thin cloud of gas and dust, but is otherwise "at rest" (relative to us), will appear redder because most of the attenuation occurs in the blue light. However, its "hydrogen forest" will still be at the same wavelengths. There is no redshift.
A star that is moving away from us will show its hydrogen forest at longer wavelengths. If, in addition, that star is seen through a cloud of dust and gas, it may also be attenuated and appear redder.
The two are two separate effects and they are easily distinguished from each other.