You can usually tell by the ingredient list though if the majority of the protein comes from animal or plant based ingredients. If you compare Orijen to Ol'Roy (Just using those two to show an extreme difference).
Orijen:
Fresh boneless chicken*, chicken meal, fresh boneless salmon*, turkey meal, herring meal, russet potato, peas, sweet potato, fresh boneless turkey*, fresh whole eggs*, fresh chicken liver*, fresh boneless lake whitefish*, fresh boneless walleye*, sun-cured alfalfa, pea fiber, chicken fat (preserved with mixed tocopherols), organic kelp, pumpkin, chicory root, carrots, spinach, turnip greens, apples, cranberries, blueberries, licorice root, angelica root, fenugreek, marigold flowers, sweet fennel, peppermint leaf, chamomile, dandelion, summer savory, rosemary, vitamin A, vitamin D3, vitamin E, niacin, thiamine mononitrate, riboflavin, d-calcium pantothenate, pyridoxine, folic acid, biotin, vitamin B12, zinc proteinate, iron proteinate, manganese proteinate, copper proteinate, selenium yeast, Lactobacillus acidophilus, Enterococcus faecium.
Ol'Roy:
Ground Yellow Corn, Meat and Bone Meal, Soybean Meal, Chicken By-Product Meal, Wheat Middlings, Animal Fat (Preserved With Bha and Citric Acid), Natural Flavor, Brewers Rice, Salt, Calcium Carbonate, Potassium Chloride, Choline Chloride, Color Added (Titanium Dioxide, Yellow #5, Yellow #6, Red #40, Blue #2), Zinc Sulfate, Vitamin E Supplement, Ferrous Sulfate, Zinc Oxide, Niacin, Copper Sulfate, Vitamin A Supplement, Biotin, Manganous Oxide, Calcium Pantothenate, Vitamin B12 Supplement, Thiamine Mononitrate, Pyridoxine Hydrochloride, Menadione Sodium Bisulfite Complex (Source of Vitamin K Activity), Riboflavin Supplement, Sodium Selenite, Calcium Iodate, Folic Acid, Vitamin D-3 Supplement, Cobalt Carbonate.
The only real high protein plant ingredient in Orijen is peas, and it's pretty far down the list.
In Ol'Roy corn is not especially high in protein (about 10% on dry matter basis from what I've read, I could be wrong). Meat and bone meal is an animal source. Soybean meal is over 50% protein- I bet that's where the majority of the protein is from, soybeans and unknown animals. These are the second and third ingredients.
Even if the water is not added to the kibble, the animal will usually make up most of that in drinking later. As digestion occurs everything is kind of a slurry- it's not digested dry (obviously). I feel the only way you can compare the nutrients between raw and kibble is on a dry matter basis.