I've just seen the first few technotes coming out relating to Enterprise Vault 10.0.3 (not quite released yet it seems) and Exchange 2013. Here are links to each of them:
TECH200516 - Exchange 2013 items with attachments archived via the Content Management API cannot be exported to PST using Discovery Accelerator, or viewed in Outlook using Archive Explorer
There is a registry key to 'fix' this. The key has to be put on the Enterprise Vault server.
TECH199617 - Users temporarily lose Enterprise Vault functionality after their mailboxes are migrated to Exchange 2013
Looks like it is fixed after the next mailbox synchronisation activity from the Enterprise Vault server.
TECH199616 - Enterprise Vault Exchange archiving tasks fail on startup when targeting Exchange 2013 in mixed Exchange 2010/2013 environment
Can be fixed by moving the Vault Service Account to Exchange 2013, or by enabling RPCClientAccessServer to talk to an Exchange 2013 server (rather than Exchange 2010)
TECH198553 - Enterprise Vault archiving tasks experience connection issues with Exchange 2013 targets
Looks to be a Microsoft issue where sessions aren't counted correctly.
HOWTO83265 - Excluding Exchange 2013 health messages from the journal mailbox
Looks like it can be worked around with either an Exchange journal rule, or selective journaling on the Enterprise Vault side.