I say it's very useful. As long as it isn't 100% cnp it still could serve its purpose. We map makers do have the regular Blizzard icons, yes, but sometime you may want to do something with just a minor change. A regular blizz icon in another colour or with just some small changes to it could do it for you. For example, I may want to create a roar in icy blue for let's say an ice bear unit. Instead of using the regular roar model (which, believe it or not, is orange and red) with its default icon, the blue roar with Mr.Goblin's great modified icon here could give a much more professional and graphically appealing feel to it.
I think that both map makers and players would find it cool and useful if we had more blizz icons with just simple minor changes. I for one doesn't care if it's cnp or not as long as it fits in my map, and if the modifier of the icons actually doesn't take credd for it that should be okay.
I see why people that make great icons from scratch should be appreciated for their work and I doesn't say all cnp should be accepted, but I actually don't agree that cnp should be banned, slaughtered and hated just because it's not a fully freehand made icon.