I worked there, and yes, most of the server side stuff is in Java and Go.
Do you need both or would just Go do :) ?
Hate Java
If you were starting from scratch, you probably would start with a different system. However web objects was their web framework at the time which was ported from objective c to java decades ago and shifting legacy from any technology to another is practically impossible especially if that technology is a cost rather than a product.
I am not sure what is upsetting about the question was honestly wondering how realistic it is to work at Apple on services using primarily Go.
Disappointing but perhaps not surprising. Your experience is reasonably recent?
Either you ask someone who worked there, or you can trawl job postings.