The boy in the striped pyjamas is a shit story, completely implausible and very patronising in its attitudes towards the victims: don't see why it would be an essential part of understanding about the Holocaust at all.
What Cory says - it's unoriginal, unbelievable (no way would the child of a guard, let alone the Kommandant, be allowed anywhere near the inmates of the camp), patronising, over-sentimentalised crap. However, I doubt that anything it portrays will upset most children (though if your son is very sensitive it may affect him). It really doesn't show any of the horror (thank God, as they are showing it to young children) - just hints.
I don't know if you've seen it, but I think it's on YouTube if you want to watch it yourself first and make your judgement over whether your son could cope
Sentimentalising the Holocaust is insulting to the victims. Two excellent books for children are "The Silver Sword" (Ian Serrallier) and "I am David" (Ann Holm). These are empathetic without being patronising, and reading about this period in (factually accurate) fictionalised accounts may be more appropriate for your son. Reading also gives your child a chance to put down the account if it is too distressing (though these are well written children's books, and don't overstep the mark in any way) and to ask questions or make comments as he is taking in what is happening.
It also gives you the opportunity to help his understanding of this horrific period (Holocaust Memorial Trust has suggested some ideas fro discussion around "The Silver Sword" and possibly "I am David", too.)
hmd.org.uk/sites/default/files/the_silver_sword.pdf
Both books have been made into films, but I haven't seen them so can't comment.
I would err on the side of caution if I were you. If he decides he wants to watch it (perhaps after his classmates have talked about it), you can always get hold of a copy somewhere.