I am from Argentina, "hispanohablante" sounds natural to me, while "hispanoparlante" does not (however I think it is fine). "Castellanohablante" and "Castellanohablante" sound really bad to me, I am not sure if it is even correct.
There are some exp<b></b>ressions that change in Uruguay, like "pronto". In Uruguay "pronto" means ready; like "estate pronto" (be ready). And in Argentina "pronto" means "fast", so then I do not know if it can be different in Uruguay.