It shall forever be a mystery....
It makes sense that some of the storyboards appearing online wouldn't be in the show. But big things like Heather, and Stoick's dragon, and "Alvin's Dragon Training Cage"? Well, those are pretty critical to the plot. You can't just take them out. Unless Alvin is being renamed to Frederick or something.
So I'm going to guess the answer is yes. Alvin will be appearing.
Oh, and by the way, John Sanford actually is, in fact, interesting. Besides working on the Dragons TV show, he also makes some really great webcomics. You should follow him.