Haven't read through the whole thread yet, but in case no-one answered this. I created other calendar under same account in mail system, and both original and the test one were synced to the phone with their respective calendar names and meetings.

Note that the system I tested with was Zimbra Network Edition (that supports active sync), and not a native Exchange. Mileage may vary with Exchange systems. But at least the client does seem to support multiple calendars with one account.