I suppose that if you were pointing a subdomain to a wikipedia article which related to your company on an open wiki it could just become a vandalism magnet for your competitors or clients you have managed to upset.
In terms of Search engine optimisation the direct wikipedia URL would always have preference to a subdomain anyway. I'm also led to believe that redirects aren't listed by google because they see it as a way of gaming the ranking system.
Slightly OT, I know some wikia sites have a shorter URL for convienience, but as Luna points out that also has *"...Issues of page ownership". *Before the fork, it was pointed out how many tinyurls point to wikipedia, so in that respect you could say that the whole issue is moot.
mike