If I forget Yaaleh ve-Yavo and am davening with a minyan, to I have to repeat it or can I rely on the hazan’s repetition of the Amidah to be motzi me?
You should preferable daven again, and not rely on the Chazan’s repetition.
The Shulchan Aruch (124:10) writes that one can rely on the repetition, provided one focuses on his words, and does not interrupt, just as a regular davening. However, the Mishnah Berurah (40) writes that today, it is better to daven again, because it is hard to focus for the duration of the Shemoneh Esrei on the Chazan’s repetition.
In addition, one cannot rely on a Chazan who does not enunciate the words clearly.