When you join a team, the team is counting on you being there and participating to the best of your ability. If due to other commitments you are unable to be counted on then you should not be on that team.
I am not a fan of any sports team that makes a year round commitment mandatory, especially for kids who aren't even in HS yet. How do kids figure out what they like if they are only allowed to do one thing. Sure they love it, its their only option.
I don't know if there would be any conflicts. Maybe there would be... maybe there wouldn't. My DD wants to play school sports other than softball, but in her mind softball and her TB team comes first. Basically, she wouldn't have a problem missing a school sport for softball. She considers herself a softball player who can plays other sports. After volleyball practice (middle school) she goes home and works on her batting or pitching... not her digs, sets or serves.
From some comments it sounds like HS soccer/ volleyball/ whatever in season if you are on the team should be the priority, even if you are really a year round softball player, and if you can't commit to the school sport %100 or make it the main priority then you shouldn't do it as it isn't fair to everyone else. While I definitely get the team concept, I want to think if her coach/team know what her priority is and if she is willing to accept consequences for missing things then she should be able to play both and just take whatever consequences are given. If she needed to study for a test instead of volleyball practice or a game; she would definitely miss the practice or game. (I doubt I could keep her out of a softball game without a fight and tears).