Is this social etiquette the same in America and American people say
"Good morning" to their roommate everyday?
It depends. Some people aren't morning people at all. They usually don't care for good mornings because it makes them upset that they are awake and still not sleeping.
However, as long as the roommates aren't totally awkward with each other, I'd say it's OK.
Remember the rule that "what words you say generally don't matter, it's HOW you say it, and how it makes people feel that matter".
So use a good, polite, energetic (but not fake enthusiastic) tone when saying good morning.
Sometimes a person may just be unhappy in general, like having depression, which is very common in America. Do not worry about this though. Still be polite, happy, and real to them and say what you want. Use good tone and manners. In time, they will hopefully be able to become happy again, and be glad it's a new morning.