Yes, you can use nectarines – it’s great!
I don’t bother to peel the peaches. Long live the vibrant, colorful, fiber-rich peach peels!
If you don’t have a lime, I’ve made this with vinegar in place of the lime juice and it works great. You just need some kind of acidic element. I used white balsamic vinegar but apple cider vinegar or champagne vinegar would also work.