I can answer the first part but I don't know the second part for sure. For large breeders If a chinchilla is separated from the female due to due to sickness or death before it is weaned it is the preferred method to put it with a lactating female. In most cases it is the only way an orphaned chin can survive. Although it's possible to hand rear it it is rarely successful.
I'd imagine it will prefer its biological mother over another. That is how most animals are, and under the right circumstances baby animals will try to suckle on just about anything.