Dandruff

http://www.dorwest.com/

Not the cheapest around but they are good quality  and designed specifically for dogs.  I have used them for Beau since I got him at 13 months old.  I would also try giving him a daily brush.  Nothing to harsh but it will help to stimulate the production of oils and help the dry skin that way.  You could also try adding some tinned oily fish such as mackeral to his food once a week or so. If the dry skin is very bad or as a sort of sticky texture to it get your vet to check it out as there may well be another cause.

As far as the patches around the eyes are concerned this again appears to be normal as Beau's got them as well, although Diesel does not so I suspect that this again may be something to do with colour.  Blues and Blacks do tend to be slightly different than other whippet colours with regards to coat.