President Carter,
From what we have learned, there seems to be no issue with "assigning" a time zone to a bunch of clients. If you are not sure where some of the clinet s are, assign them a timezone based on your best guess and run the tool. What happens (in our lab testing) is that Outlook actually displays things correctly once the client has logged on. Note that this is coming from what we have seen in support cases. I would suggest you test this for few test mailboxes and assign them a "wrong" timezone to make sure that nothing out of ordinary happens. Create a "complex" mailbox meaning if there are 3rd party mobile devices, OWA access etc, make sure this mailbox does it.