Enterprise Vault could definitely assist in this process, however using EV just for a migration tool and not being used above and beyond that point, i'm not sure whether its cost effective for you. Definitely contact symantec who can tailor the licensing and possible solutions to your needs and possibly demo what it can do and how it can help.
Domain migration and exchange migration with EV is definitely very plausable.
However you may find you have to do some stuff manually later on, in regards to attaching the new users mailboxes in the new domain to the EV Server.
If possible if you could install EV in the destination (i.e. the domain you will eventually end up in) and then target the exchange in the old location, that would definitely make it go smoother.
https://www.linkedin.com/in/alex-allen-turl-07370146