i use kelp as part of a DIY supplement mix for my own dog.
it's true that it contains iodine, and also a wide variety of other nutrients in a natural form. however, it is very easy to supply too much and in the case of iodine that can have serious side effects, such as thyroid problems and an impaired metabolism. for that reason it's important to know just exactly how much iodine the product contains, so you can measure out a daily dose. as per the 2003 NRC recommendations, 15 microgram per kilogram (2.2 lbs) of body weight is all that is needed.
fish is fine to feed to dogs, even whole fish, bones and all. one thing you need to be aware of is that fish of the salmonid species in the northwest pacific can contain a fluke which can make dogs seriosuly ill. this can be avoided by thoroughly cooking the fish tho.
http://www.vetmed.wsu.edu/ClientED/salmon.asp
antjen78, would you list some of those foods you think would be excellent for one breed but not for another, and the reasons why? i know that different dogs have different nutrient requirements, but i'm not aware of any items that one breed could eat while another can't. (and i'm not talking about genetic diseases like for example copper storage disease.)