Well, for one I agree that Hogie has designed some great stuff.
Believe it or not, artists (and fans) sometimes have ideas that can be very similar, if not the same. For instance, one person recolors a hat, and another person gets inspired to do the same...
In this case, there are many "experiments," but there are certainly a handful that are more popular. So, it is not inconceivable that more than one artist might have similar ideas, or even similar designs (since, after all, Sparky looks like Sparky). In all honesty, it doesn't really matter who took the time to design this particular hat first - both artists were inspired by their love of art, and their love of Disney/Stitch.
However, since there are many people who feel that Hogie is somehow being wronged by this hat being released and no credit going to him, I'm including a picture to show when Tink first created the Sparky Hat, as well as when she updated it to finally be released in the game. I blocked out my name from this picture because, well...it's my real name.
@hogie - keep making stuff! You're a great artist!!