The way ratings system work, they rate the game content the Devs make. They don’t rate the Player created content (names, chat, etc.). The Player created content has to go by the company polices, which are very family friendly.
If you would not say it around families of all ages at the town fall festival or church picnic, don’t use it. The Forum Code of Conduct is a pretty good place to start reading - it goes into detail about the types of things Blizz does not allow.
Also, just because some limited filters don’t catch something, does not make it ok to use.
And here is the Game Code of Conduct which covers all Blizzard games equally. Blizzard Support - Blizzard's In-Game Code of Conduct
Blizzard games offer a fun and safe place to interact with one another across various game worlds. We encourage our players to cooperate and compete in our games, but crossing the line into abuse is never acceptable. If you come across a player violating the policies below, you should report them.
Communication
When participating in communication of any kind (chat, voice communication, group finder), you are responsible for how you express yourself. You may not use language that could be offensive or vulgar to others.
Hate speech and discriminatory language is inappropriate, as is any obscene or disruptive language. Threatening or harassing another player is always unacceptable, regardless of language used. Violating any of these expectations will result in account restrictions. More serious and repeated violations will result in greater restrictions.
Naming
Names are subject to the same rules established above. Any name the player has the ability to customize—such as player names, BattleTags, and guild names—must be appropriate and inoffensive. Any name that violates our standards or disrupts the community will be changed, and additional limitations may be placed on the offending account per our discretion.
Take note that acceptable names are determined by player reports and Blizzard’s decision, and role-playing servers may have distinct standards for using game-appropriate names