When importing customfields with Totara sync, with a custom field of type date, the date is imported but it is not enabled. To see what I mean, see this screen shot:
Hence, the hire date is not available in this case to be used in audience rules, etc. The date gets imported but is not enabled.
This is Totara 2.5.5
To reproduce, just create a user date custom profile field, and try to import it with Totara Sync. After successful Totara Sync run, check out the user's profile via the UX. You will see as per the screenshot above.
I had originally reported this as a bug #964
Expected behavior would be for the date field to just be enabled. Why would you even want to "disable" a custom user profile field, not sure.