Really? I've seen a lot of fire suppression systems and all they had was the automatic sprinkler valve separating them from the potable water system. Maybe they don't do it that way anymore and maybe the ones I saw were grandfathered. At any rate if the fire suppression system is filled with potable water I think the comparison IS valid.
Even if I am totally nuts about the comparison of fire suppression sprinklers to a dead-ended pipe in a potable water system in a residence, how about giving an answer to the original poster?
Fire protection systems are required to have backflow prevention installed. If it has not been enforced in your area inspection is lax. In the picture below the grey device is a backflow preventer.
Legionella is present in water supplies in low amounts and it is not killed by chlorine in the levels used in water distribution systems. It is not usually a problem unless it spends time in a stagnant location at thr prime growth temperature.
Dead end lines over a certain length are prohibited by code. Check the code used in your area to determine length. They can present a problem of biological growth in the system.
You are correct air chambers are ineffective as hammer arestors. The air in the chamber is both absorbed into the water and dispraced by water movement. Piston type hammer arrestors should be used.