This is more a Microsoft than a Blackberry question, but I'm thinking not.
Exchange is built to work with Active Directory, and that does require at least an internal (i.e. Microsoft-defined) domain. But even though it's built to work like that, I'm not sure that means it requires one. But even though I'm not sure, I think it does require a domain.
A thing moderately good is not so good as it ought to be.
Moderation in temper is always a virtue,
but moderation in principle is always a vice.
Thomas Paine, "The Rights of Man", 1792