Working with athletes is like working with any group of people. You've got great ones, terrible ones, and everyone else in between.
I've worked in different profesthingsional organizations and have seem them all.
My first career in sports, I actually had to deliver game tickets to players every week. Some of the Pro Bowl caliber players were real jagoffs behind the scenes even though in front of the cameras they were saying all the right things. However, there were other players who would eat lunch with me, and engage me in conversations other than football. Had one player give me a pair of shorts he had gotten from a shoe company just because I was dedicated to making sure the guys got their stuff on time. Some were good in spirit and would laugh & joke with me all the time. I had one guy (the pro bowler) who was a jerk 90% of the time. I pretty much ignored him.
Depending on who you work for, may determine what interaction you can have with the athletes. I worked for one team and their policy was we couldn't ask for autographs and if you got caught doing so, then you'd be fired on the spot. However, even then there were some good guys on the team and we would sit around chatting up on life.
I'll say this much about working with and around athletes. Even though some can be real jerks, most are just like you & me, they just get paid more money to work. While you may not become best friends with them, most of them will treat you well. At the end of the day, it can be some great experiences.