I think all your questions are absolutely valid and I have been asking myself the same.
Can nursery see a pattern to his hitting?
Does he do it in the afternoon when tired or before lunch when hungry?
I keep asking this but they seem unable to be specific when I ask.
Although a lot of incidents happen before or at meal times.
Is he doing it when someone takes something off him or has something he wants?
A few times (minority) this was the cause. I'm not too concerned about those events. The children need to learn to live together.
Most of the time they tell me they don't know why or it's out of the blue.
Is he doing it to get another child's attention?
This has never been mentioned.
Is he always cross when he does it?
I don't know.
Does he do it anywhere other than nursery?
He can have huge meltdowns or stand offs when with us too. But again some of those happen when I pick him up from nursery and they reported hitting others.
Does he do it in the afternoon when tired or before lunch when hungry?
Are there any concerns about his speech or hearing?
I don't think so. I have to declare that a few months ago my son's eyes started turning in and no one said anything. He now wears glasses (a strong prescription according to the optician). This is one reason I'd prefer someone external to see him because if the nursery completely missed something that I believe was obvious, what else are they missing?
The hitting has been going on for 4 months and only now have I been formally called for a meeting with the managers.
The strategies they now mention are reinforcement of positive behaviour + learning that bad behaviour has consequences by removing "privileges" (such as not being a helper or skipping an activity).
Finally, although I understand children can hit, the other children this age I know do not do that on a regular basis and so yes, I find it concerning (not least for the children my son hits).