It's exactly because jockeys are independant contractors, who must be to perceived by the public as representing only the interests of the connections of the horse they are riding in any particular race, that it is a bad idea to allow jockeys to sport advertising on their silks.
For inevitably a conflict of interest scandal will arise. Jockey A, wearing advertising for a particular company will make a bad move on the track and get nosed at the wire. By a horse it turns out whose owner has major holdings in the company whose advertising Jockey A is being paid to wear.
Now I'm not saying that Jockey A necessarly did anything wrong. A lot of owners have a lot of business interests and it was probably just an innocent coinicidence. But in racing, because of the gambling aspect, perception is reality.
And so now what? Owners are going to have to disclose all their financial holdings, and the holding of their immediate family members, to the Racing jurisdictions to insure there are no conflict of interests?
I don't think so. And in fact, I can think of nothing that would drive established money out of the game quicker than if reporters started investigating the owners finances every time they won a race.
But on the other hand, maybe there will be races where the jockey's aren't so innocent. After all, it does seem to me that a sponsorship deal is a pretty clean and efficient way to launder a bribe.
No, jockeys must be held to a different standard of commericial ethics than other athletes because, well because they are jockeys. The definiton of their job demands the perception of complete allegiance to the connections who have hired them to ride in any particular race. Lose that, and they probably lose the public.