Phoenix, there's no current version of Outlook for Mac. There was such a thing a long time ago, but it was replaced by Entourage. The new Outlook for Mac will replace Entourage in turn.
As I understand it, however, Outlook for Mac will not support CalDAV. I would expect it to support IMAP, just as Outlook for Windows does, but for other server interactions, all I've heard about is Microsoft's proprietary Exchange Web Services. This is the same interface used by Entourage 2008 Web Services Edition and by Apple Mail.app when connecting to an Exchange server.
The issue of EWS support is tracked under
Bug 38631 - Enable snow leopard messaging features, Outlook for Mac 2010
As far as iSync support, I couldn't say. However if you look at what happened to Zimbra iSync with Entourage and Mac OS, I wouldn't keep my fingers crossed.
I would dispute the premise of the initial question, though. We don't know what most business users with Macs will use for email once Office 2011 is released. Right now at my company, they use Mail.app to talk to Zimbra, and they'll happily continue to do so. I imagine if a business has an Exchange server, or possibly (eventually) Kerio, they'll have a choice of Mail.app or Outlook 2011.