Text from Wikipedia is can be used on your website if you comply with the Creative Commons Attribution-Share-Alike License 3.0 under which the content is licensed. For the full list of requirements see the licence itself. The highlights are:
- You must link back to the Wikipedia article that is copied.
- You must list all authors.
- If you make modifications, you must indicate that that it has been modified.
- You must licence your modifications as open content under the same license.
Syndicating content from Wikipedia is generally not going to help you get traffic from search engines:
- The content will be identified as duplicate.
- The pages with the copied content will likely not get indexed on your site because the search engines will prefer the more authoritative source (Wikipedia itself.)
- If your site has little original content of its own, the entire site could be de-indexed as a "scraper site."
For more information see: What is duplicate content and how can I avoid being penalized for it on my site?
Search engines usually don't care much about what software powers a site. It isn't going to make much difference if your content is powered by wiki software or hosted as articles. If users prefer it in one format over another, then use that format. For example, if your users expect to be able to edit the content, then the wiki format would be preferable.