Whole hemp seeds have a tough outer shell. If they aren’t chewed extremely well, they can pass through the digestive tract undigested, meaning you lose access to the protein, omega-3s, and other nutrients. Grinding breaks the shell and exposes the nutrients, which increases absorption.
Grinding slightly increases exposure to oxygen, but the effect on nutrient loss is slow, especially if you grind only what you’ll use soon and store in the fridge or freezer.
Re the ground hemp seeds - if the grinding affects the heart itself, doesn't that release some of the nutritional benefits of the hemp hearts too early and because of that reduces the uptake of the beneficial substance? I've heard not to grind hemp until ready to use. thanks