I always add fish oil to all my dogs' diet. We use human grade fish oil supplements making sure they are 100% fish oil with no soy added and checking for EPA/DHA levels. It's the same thing as oil supplements targeted for dogs, but so much cheaper - something that's of great importance for us with a household of four dogs. The dogs also get a meal of salmon usually twice a week.
I believe Yumega primarily uses flax to obtain its omega 3's, and dogs cannot process the oils from plant materials as easily as they can from fish. Not saying that they can't, but it's a much more inefficient and you probably don't get near as much the benefit from the same amount of fish oil.
I'm not nearly as interested in skin and coat condition as I am in the possible cardiovascular, anti-inflammatory, and neurological benefits dogs can receive from consuming omega 3s.