What do you consider “normal”.  The rears will be configured as surrounds.  That means they will be playing surround effects like ambient noise (crowd sounds, rain and wind, soundtracks, etc.) and/or directional cues (bullets flying by, planes/cars passing by, off-screen voices or sounds, etc.).  They won’t be playing a repeat of what the Beam is playing, because surrounds have completely different channels from the front left/center/right or Atmos channels.  

And One SL’s would be a cheaper option, you won’t miss the One’s microphones since they aren’t used when set up as surrounds.

You can add a voice assistant to either, or both, Sonos One surrounds these days, in addition to the Beam.

Thank you. I wasn't sure how to word the question but just wanted to make sure the Beam would still be play Dolby Atmos 

The Beam can interpret a Dolby Atmos signal. It does not have separate height channel speakers like the Sonos Arc does, so it will interpolate the Atmos sound from the front. It can pass the Atmos signal to a pair of Era 300s set up as surrounds, which will help maximize the Atmos interpretation, as the 300s do include extra speakers to help direct the Atmos signal. 

Wow. Never noticed this, but you are right: