I agree- maybe just ask that his full name is written on things. I've never heard of Ally being used as a boys name so I can understand how he's feeling uncomfortable in an Australian school with Ally written on his things.
That's exactly right, I know how difficult school can be so if his nickname is causing him issues I want him to feel that is something he has control over and can change, and not feel pressurised because it's a name we like.

I will speak to OH about this another day though, his immediate reaction was "don't be silly, of course Ally is a boy's name"