Late getting into this thread and have not read the 7 pages of replies but I will chime in based on your original post.
Back when I was blue-pilled and married, my wife left me for one of her male buddies who she then entered a multi-year LTR with. I never thought he was a threat because he was a 4 and she was an 8 or a 9. They barely ever hung out and she almost never talked about him. You just never know with women.
The girl I just dated for a year and recently broke up with had a lot of beta male orbiters. I didn't feel threatened by them because none of them were anywhere close to her in looks, but that may have been naïve on my part given what happened with my ex wife. I'll never know for sure if anything happened with her and any of those guys but I have reason to believe something did.
At the same time, you can't control women either. If a woman wants to cheat, she will cheat. However, I do think that drawing clear boundaries is important because it accomplishes several things. First and foremost is that it forces her to ACT and make a decision on what is more important, seeing her male friends 1:1 or being in a committed relationship with you. In my book, no person in a committed relationship should be spending time 1:1 with someone of the opposite sex. That is a boundary for me and it applies to me equally as it applies to a girl I'm in a relationship with. There are some women who won't accept that boundary, and will try to label me as insecure or controlling for it. That's ok. Those women can go date someone else instead of me. Second is that it reduces the chance that an emotional affair happens, which can then lead to a physical affair, and it reduces the chances of someone meddling in your relationship. If a woman WANTS to cheat, she will, but if your boundaries remove her from the types of situations that evolve into an affair or cheating, it does reduce the risk. And it's also very important that you are standing up for yourself - by setting these boundaries. Good women will respect your doing this.
If you aren't exclusive with a girl, then I wouldn't bring up male friends. I just take note at the stage in the dating process as to if she has any male friends and if so, how many, and how close they are and compare and contrast the same for her female friends. The more male friends she has and the fewer female friends she has, the bigger the red flag. I have learned not to enter exclusive relationships with women like that. But if she asks to be exclusive, and you really want to be, then that would be the time to bring up the guy friends and how you couldn't be in an exclusive relationship with a girl who spends time 1:1 with other men - it's just not what you are looking for.
Because you said you were concerned with how bringing up her guy friend(s) would go, and that she would react negatively to it, I will say that I have learned it is VERY important to form and communicate your own boundaries without thought as to whether a girl is going to like them or not. You can't worry whether or not she will like your boundary. You simply state your boundary and if she doesn't like it, you walk away and never look back.