Veritas cluster migrating to a new array.

You can do online using volume manager mirroring at volume level and in terms of I/O traffic this is no different to mirroring at a LUN level using the array.   If you use array mirroring then deport and import of disk groups should work fine.  If you are concerned about the amount of work mirroring at a volume level,then you can use VOM - see extract from http://origin-symwisedownload.symantec.com/resources/sites/SYMWISE/content/live/DOCUMENTATION/7000/DOC7473/en_US/vom_ms_addons_users_6_1.pdf

Enterprises frequently need to move (migrate) storage volumes to new disk
enclosures. Volume migration can be time-consuming and complex. Storage
Provisioning and Enclosure Migration Add-on simplifies the complexities so that
you can easily migrate volumes between disk enclosures.
Using the Management Server console, you can migrate volumes in the following
ways.
See “Migrating volumes by host” on page 216.
See “Migrating volumes by enclosure” on page 219.
See “Migrating volumes by disk group” on page 221.

Mike