A few barriers to entry for doing that on a grand scale - there's already plenty of non-player-specific jerseys for dogs. Payton's got a generic #00 'hawks jersey. What's lacking is player-specific ones and/or authentic/throwback ones, and for those you're gonna have licensing issues.
Now if you want to do more of a mom & pop operation where you master how to tailor an existing jersey for a dog, that could work, but price point will be difficult. People will have to spend $30-150 on the jersey before it'd even get to you.