Neither move archive nor any of the other third party utilities will migrate FSA data, you'd have to restore the data back to its primary location and re-archive it all

If you want to see of a third party would help, I would suggest Quadrotech as they have the experience and expertise in FSA, they currently have several FSA tools already developed but their migration piece is really centered around migration of physical file servers as opposed to EV to EV migrations

You can find more at http://www.quadrotech-it.com
Or you can ping Wayne Humphreys on this forum to get some dialog started

Otherwise you have two options

1. Restore the data back, decommission the second environment, archive in to the regular environment

OR

2. Migrate the email archiving environment in to the FSA environment using Move Archive or a third party tool such as Tranvault, Archive shuttle. Akaibu etc

The difficulty with the second option is if you use to Discovery Accelerator and use legal holds, you will have to remove them, move the data and then recreate and re run the searches in the new environment

Also there is a webcast tomorrow at 11am PST that Symantec is presenting around migration best practices and may give you some good insight and ideas