First of all you need to find out WHY the rockers were hitting the retainers, too much valve lift? rockers that aren't made properly...etc. I would say yes, you probably can smooth them out but I wouldn't take the chance, have them checked for proper ratio.
Also think about where the material is that used to be on the rockers????...circlating around through your engine? Yes you can reuse the standard nuts but why bother, they are very cheap. Polyloc's are reusable....and your last question...what isn't made in China.