FF offers a substantial benefit at high ISO, and church interiors where flash isn't permitted mean you need high ISO. For static and slow-moving subjects, the 5DII's AF is fine (well, the center point is, and the outer ones in decent light). Personally, my issues with the 5DII are the poor servo tracking for somewhat faster and unpredictably moving targets. Brides and wedding guests don't usually fall into that category (if the bride is running, things have gone terribly wrong...). The center point will do well in dim light (better than the 7D, in my experience), and at the reception and other events you can mount a flash (if only for the AF assist).
For weddings and events, portraits, etc., I think the 5DII's AF will be just fine. Running kids, agility dog competitions, etc., not so much - there, if you want sufficiently capable AF and the ISO benefits of FF (indoor sports, dance recitals, etc.), a 1DsIII or 1D X is a better option. But they're expensive, and if personal or business budgets don't support that, compromises are necessary.