CrossOver respects the Region setting of the Formats tab of the Language & Text (formerly International) preference pane, except if it's set to Custom. That is, if you select one of the presets in that pane, CrossOver will format dates and numbers according to that region. If you customize the format manually, CrossOver will probably not format dates according to your settings.
You can also customize the settings using the Windows registry. Use the Run Command dialog to launch "regedit" for the bottle of your choice. Within regedit, navigate to HKEY_CURRENT_USER\Control Panel\International. There, you can set the format for dates and numbers.
Even when CrossOver properly detects the locale formats as set in Language & Text, some Windows applications ignore them. Instead, they rely on the primary language of the system to decide how to format dates and numbers. So, make sure that the Language tab of the Language & Text preference pane lists your locale-specific language. For example, it might just list generic English for a user in Australia. That user would be best served by clicking the Edit List button and adding Australian English to the list and making sure it ends up at the top.