LOTR tag wiki has a long write-up that ends with "From: The Lord Of The Rings on wikipedia". I didn't check whether it was fully copy/paste as the sentence seems to imply, but in general; is simply copying a long couple of paragraphs from Wikipedia OK for tag wiki texts assuming it's attributed?
First, if it's not attributed, it's illegal. This goes for the excerpt too, which does not have room for an attribution.
When it's attributed, it's legal, and there is no outright policy against it, but it is often not a good idea. Wikipedia is a generalist encyclopedia, whereas our tag wikis should contain information that's relevant to our community of SF consumers. For lord-of-the-rings, it's not catastrophic, but it's not very good either. For authors, this tends to be worse: we care about what they've produced, Wikipedia copy-paste tends to produce irrelevant biographical details.