The Da'shain described it (perhaps metaphorically) as the Nym taking the threads of the Aiel and Ogier Singing and weaving them into a dance.

What Rand did appeared to combine the effects of Da'shain and Nym into a single process. Rand as the Dragon was "One with the Land". The effect of his Singing were much like that of Da'shain and Nym together, but it's possibly unique.

It's also been suggested the Nym were uniquely skilled because featuring genes from trees, plants and humans and Ogier, they were able to react and interact with both Ogier and Da'shain/human Singing, which perhaps optimized the effects of Crop Singing (Rand made things grow, and his presence forced the Shadow's touch back. We don't know for sure it also made nature over productive or impervious to any disease, which Crop Singing both did). It also doesn't mean a human channeler might not be capable of using Aiel but not Ogier Singing or have very similar but not as powerful effects, or that if a channeler was of Aiel blood he couldn't both Sing and weave his own Singing threads....