The sauna scene is definitely bordering on that, it's true. Two things to consider, though. For one, it only happens on Sage's route so every other MC is innocent of that "crime". It's also easily avoidable for a "true bro" MC if he speaks up about Maya when prompted. Second, Derek never actually expresses any interest in dating Ashley, the MC and Maya just kind of assumes it before class until he starts to openly stare at Cathy's butt and snaps a photo which makes it clear that Derek isn't all that serious about her. If anything, the bathroom sex with Camila is a worse offense in regards to the bro code since Derek does rave about her a lot.
As for Derek's "game", if Maya is to be believed then Derek hasn't been successful with the ladies at all and it's not for the lack of trying. He shoots at every opportunity but rarely scores. Honestly, which of the other 4 main LIs could you imagine responding to that positively?