Is it possible to identify the source of a protein hydrolysate
DNA is not a protein, as @MARamezani states. See http://www.answers.com/Q/Is_DNA_a_protein.
There is a prevalence (or lack) of some amino acids in certain sources. For example, maize ("corn" in America) is deficient in tryptophan and lysine, so if your sample is short on those two, it is more likely that it is from corn. A list of some foods and amino acid content is at http://www.ljhs.sandi.net/faculty/aquesnell/Biology%20Notes/Chapter%204/4.8-4.13/Essential%20Amino%20Acids.pdf [there appear to be some errors, though]. According to that source, yeast may be deficient in phenylalanine, so that is another indicator.


You would need an analysis of the relative abundance of each amino acid, some reference showing their abundance in various sources, and additional analysis to calculate relative abundances in a mixture, e.g. corn supplemented with yeast hydrolyzate.