My company has employees in different time zones, but since you can only
configure Java to use one timezone, we can only make one group of users see the
"right" time from hudson.

You can detect the timezone from Javascript
(http://onlineaspect.com/2007/06/08/auto-detect-a-time-zone-with-javascript/),
so I suggest the following approach to using a user's timezone:
Detect the browser's timezone on the first page load
Set a cookie with the timezone in it
On subsequent page view, use the timezone stored in the cookie. Fall back to the
system time zone.