You are the expert on your child, and you have the best sense of how the school is doing. But if you are interested in an alternate viewpoint... I would personally not find it acceptable to keep a child in from recess if recess if something that is crucial to his success at school (I don't know if that's true for your son or not, it is true for mine - his school was under strict orders from me to never remove recess privileges as a 'punishiment'). Doing so exaccerbates the problem, rather than helping to solve it.
I would be uncomfortable with the giving of pink slips for showing frustration in a quasi-acceptable way (ie, he slammed the books closed and used his words - which by the way - were true words - he does NOT have to do what she says) - as opposed to throwing the books, calling her a bad name, etc. I would be concerned that the teacher is not responding to his frustration in a useful manner, and is instead resorting to traditional 'teaching' methods where you just keep punishing and taking more and more privileges away until you break the child's will.
I'm not a fan of those methods, but as I said you are the expert on your child so if you feel this approach will work for him, and won't make him resent being sent to school, then by all means see how it goes. But I would recommend keeping an eye on whether the methods are really working to get him back to a place where he is successful and happy at school, because if he truly is 'shutting down', then you have a limited window of opportunity to get him back on track. Bear in mind that school staff don't have to be monsters to be completely ineffective.