You dont have to have tags to be in a BFM scrim. You do have to be on BFM vent. To get on vent with BFMs you have to have asked to join BFM and waited your turn to get on vent. Those who do wait that time and make it to vent are allowed to play in scrims.
You are correct to think are scrims must be clean and full of race. You also should know that BFMs have even tougher rules to follow in scrims and in public servers. We have scrim rules and expect EVERY BFM to follow those rules even in public servers. I can tell you the scrims are a lot of fun and it is fun to race in a place where you know everyone is following the rules.
So quickly to answer your question. NON BFMs are allowed to be in BFM scrims. They must have earned vent status to be in those scrims. I hope that helps. If you wish to join BFM because of what BFM is about feel free to apply to be recruited. We are always looking for great people to make us better. Everyday we get new great people and learn from them and grow to be better and better.
I hope that answered your question. If not feel free to post or send me a pm. I wish you the best no matter the path you take. Thanks for the question!