You get the same meat from just killing, it does not require skinning. You also get plenty of pet-friendly food from non-skinnable mobs. But the question posed is not about where to get food for your pets, it's about how to manage pet happiness, and as mend pet is a minor glyph, it is WELL worth getting for a multi-boxer who doesn't want to have to manage pet happiness while leveling up. You sacrifice nothing by using the mend pet glyph, as being a multiboxer makes almost all other minor glyphs irrelevant.