Yeah I daw that picture already several times, the only thing is that nobody really can show that this is official nintendo artwork. They're always only appearing this little part of the picture but nobody can show the source and the entire picture (not even the mario wiki).
Plus on the Super Mario World TV show in the episode "mama luigi" you see a new born yoshi without shoes and for example there wasn't any white pads or anything.
You're theory is interesting anyways and surely there is the possibilitie that it is true, but even if there's existing a official nintendo source or statement hiw his feet looks like, my perfect yoshi feet will always be without pads and complete green (what doesn't mean I don't like feet with pads XD).
But yeah that's really a difficult topic and am still since a long time eager to see the complete picture of the one where yoshi is whining about his lost shoe
Yeah I daw that picture already several times, the only thing is that nobody really can show that th