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