Hmmm.... Exchange will get real unhappy when you remove it from the domain but if you add it back to the same domain (different domain controller I assume?) it should be OK. Unity doesn't have any particular attachment to the domain itself, it's Exchange you need to worry about. If the Exchange server on our box gets fussy we're dead in the water. I have never tried replacing a DC out like this myself so I can't say with authority if it'll fly or not, however I suspect this will work OK since you're not changing the domain it's a member of, just pulling it off for a bit and putting it back.
Jeff Lindborg
Unity Product Architect/Answer Monkey
Cisco Systems
lindborg@cisco.com
http://www.AnswerMonkey.net (new page for Unity support tools and scripts)