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A few of the centers I submitted were rejected because according to the reviewer the "content" was too close/similar to the main site.
Not having experience with BizEx (yet), I can only say that the centers we have were listed as their own separate entities. As to why that is, I'm guessing the center content was specific enough (articles, books, news on each subject) to be accepted.
The centers pull in quite a bit of traffic. I'd say it's worth a try.