It definitely needs addressing, but are you aware of any of his friends expressing that they have a problem with this teacher? Or is this a class where there are several very difficult children that she has been trying to control and is raising her voice due to group behaviour? Has he said some if the children don't behave at all?
Firstly you could try and support your dss by asking what she shouts about. Is it because some of the class don't listen etc. Then explain that when this happens she is shouting because of their behaviour and he hasn't done anything wrong, so the teacher isn't cross with him personally, just a group or individual in the class who isn't doing as they should. Can he have a process you set up with him, when she shouts he thinks did I do or not do whatever it is she is cross about? If I didn't then she isn't really cross with me. She's just unhappy that someone else or a group has behaved this way, so I can feel proud I haven't done anything wrong, and think about how well I'm doing in class instead.
Talk about the language she uses, if she ends turning it in to a generalisation odd "this class does xyz" or uses phrases like "you all" or "this class" when shouting, it's because she's frustrated, or because a lot of the class are being noisy for example, so she shouts for the whole class to be quiet, even though not everyone is being noisy. It's just telling the whole class what they should be doing because it would take too long to say all the names if the kids who are being disruptive. It isn't good that she's resorting to yelling a lot, but if he can start to rationalise it he may be able to cope better.
I also agree it needs an initial approach to the teacher to raise the fact that your dss is becoming anxious about school. Ask if the teacher has noticed anything and what the class dynamic is like. Is it a class that needs a lot of work to keep all the pupils behaving. If so would she confirm he behaves well and explain he can't seperate her trying to discipline those with behaviour issues with feeling that she is also angry with the whole class, so angry with him. That is making him worried about school, so is a mental health issue, and affects his ability to learn. Hopefully it will make her aware enough to try and moderate her style.
There have always been teachers who don't realise the effect of their behaviours. I remember my mum saying she had a teacher in secondary school who used to shout at the class and throw things. The pupils were so scared they were sat waiting for his next outburst, and found it impossible to learn from him. He was shocked when a group of them got up the courage to speak to him as a group about how their learning was being affected, and amazingly changed his behaviour.
Equally there are teachers who do know and are happy to try and subdue their pupils. I had a teacher when I was 5 who got me so convinced I was bad because I didn't fit her idea of what a girl should be interested in that I developed nervous tics and nightmares. Apparently my teacher, when my mum went and spoke to her, was quite comfortable saying my worries were down to her trying to push me in to her mould of what I should be like, which was not because I was misbehaving. I preferred going in the book corner during free play, not playing in the wendy house with the other girls, and apparently this wasn't normal.
Obviously these examples were decades ago, in the mid 50s and late 60s, but people, including teachers, haven't lost the potential to be a bad fit for their profession or to be bullies over the years, although they may not actually throw things nowadays, or be do overtly sexist.