I haven't reviewed the site in question, so I can't make any very authoritative comment, but in general I'm very much opposed to this kind of link in the encyclopedia.
There are a lot of "gray area" issues in this area that we've never had to deal with in terms of coming up with a specific policy... it just hasn't come up yet. But in general, I think we should take a _relatively_ "hardline" approach against linking to non-free resources.
(Not _absolutely_ hardline, as it is useful and valid in many cases.)
My tiny little side-project http://www.3apes.com/ is an effort to create a free directory with a really free license (unlike dmoz.org, which has a partly free license) and a wiki-style community. But I haven't promoted it much nor worked on it much, so it's still more of a pioneer site than an actual live project.
It might be sensible at some point in the future for Wikipedia articles to include links taken from such a separate project, I don't know.
--Jimbo