Those hot models that constantly surround rich Instagram stars and Vegas playboys
Atmosphere Models are attractive girls who are hired by a venue (club/bar etc) to hang out with guests and participate in the day's activities. They are to dress like normal girls and are not supposed to tell people that they are hired workers
There are 3 different types of girls that we're talking about here.
Atmosphere models, Companions(unpaid atmosphere models), Escorts
Atmosphere Models are attractive girls who are hired by a venue (club/bar etc) to hang out with guests and participate in the day's activities. They are to dress like normal girls and are not supposed to tell people that they are hired workers, BUT what they do is completely legal. They are hired simply to make the venue look better because 'hot' girls hang out there. They are not hired on the basis of being a hooker or an escort. If they happen to have sex with someone after attending the event, that is individual to them and sometimes that happens. I know girls who are atmosphere models who are just normal chicks, they get paid $200 to hang out at the party, and then they go home as soon as they aren't paid anymore. I also know atmosphere models who fuck rich dudes and go on their boats and all of the above, but they don't consider themselves escorts, they just hang with the rich dudes and go on vacations with them because it seems like a fun opportunity and also...these girls sometimes want to get wifed up and get married to a rich guy. What better way to meet a rich guy than to be an atmosphere model and get paid to hang around rich dudes. Honestly this is a pretty good business venture for these girls.
There are also atmosphere model companions, these are atmosphere model's best friends and they basically do the same shit as the atmosphere models but they don't get paid to go to the party and they make sure that their friend isn't roofied or raped. They also go on vacation with rich dudes and look to marry/fuck rich dudes. it's a good business venture for these girls because they just hang out and get to go on awesome trips and do rich people things.
Escorts, These girls are hired by men to have dinner with them/go on dates/ go on vacations/ and sometimes have sex. These girls are on a mission and only see this as work, it's not necessarily for fun, even if they do have fun. Escorts are often pimped out by guys or by websites and they make money on whatever activity they do. These girls can also be considered sugar babies. Sugar babies are basically paid girlfriends.
There are also girls who aren't any of these by label, but hot girls tend to gravitate towards the best party. If you're rich as fuck and you're popping bottles in the club (like big fucking bottles), hot girls will naturally just gravitate towards your table because your table is going to be the best party in the whole damn club, but...if you're ugly as fuck and nasty and creepy, normal girls aren't going to come to your table even if you're blowing hella cash. It's not that worth it. If there's a table blowing hella cash and they're nasty and creepy, hot girls will just go to the second best party that has dudes that are both good-looking and rich.
The short answer is, some girls are atmosphere models and are totally normal, they get paid to hang around rich dudes but they aren't required to do anything sexual or anything. Its a job. There are girls who get paid to go to the party, but end up fucking and hanging with rich dudes, and then there are escorts, which are basically classier hookers.