I think it is more of a case of (in Moyes' eyes mind you) Zaha not being 'Manchester United' ready at the moment. I don't think Moyes is childish to have some personal problems against him and that's why not playing him. The tracking back is crucial in 4-4-2 as otherwise while defending we will be man down. Yes Ronaldo too didn't track back but it did cost us goals on occasions. Due to his overall genius, which is once in generation kind of, that flaw got overlooked by fans. SAF still got him to work on that aspect.
I think Ole knows what will be expected of Zaha at United, and he will mold him for that and send him back ready for next season. See, as a fans, it is not that bad scenario for us. If Zaha does very well and plays key role in keeping Cardiff up, Moyes will definitely include him more or in other words, he will have no choice otherwise.