It's a good idea but I'm wondering whether those celebrities wouldn't get annoyed knowing that someone is beating their face every single day. People would perhaps start filming the process, uploading it on youtube, etc. for others to see how they are "kicking Tyson's but". Even though those are just dolls, but I personally wouldn't want someone having my exact copy-doll to beat it whenever they want. I think most people would have that kind of reaction. Of course, someone could use anyone's picture to stick on a doll anytime and no one would know, but if we're talking about an official mass-producing company, then it's a different situation.
I'm not even sure who would get more frustrated - celebrities or regular people. Celebrities tend to value and protect their status, so world-famous fighters might dislike the idea because of that. On the other hand, at least they are used to their image being displayed everywhere. On the contrary, if someone asked to produce a doll of their life "enemy", that enemy most certainly wouldn't be happy about this, unless maybe they do the same:)
A solution to this, at least or especially in the case of celebrities could be to offer a percentage of sales to the famous person in whose image the doll is sculpted. The more people will desire the doll of a particular celebrity fighter, the more funds that person will receive from the sales. But in any case, I think this issue should be addressed one way or another before such a company could start the production and sales.