I have a domain with Win2012 DC's, and a bunch of Win2003 servers.
Is it save to raise the functional level of the forest and domain to Windows 2012?
Yes.
Member servers don't typically care what the FFL and DFL is - only domain controllers. As long as all your DCs are 2012, then go for it. And you don't have a bunch of other stuff that you're not telling us like "oh yeah and I have a trust to an NT4 domain in a branch office," or "oh yeah my org is still on Exchange 2000."
If all of the Domain Controllers are Windows Server 2012 then yes it's safe to raise the Domain functional level to Windows Server 2012. Here some guidelines from Microsoft on Domain and Forest functional levels:
You can raise the functional level of a domain only if all domain controllers in the domain run the version or versions of Windows Server that the new functional level supports.
You can raise the functional level of a forest only if all domain controllers in the forest run the version or versions of Windows Server that the new functional level supports.
You cannot set the domain functional level to a value that is lower than the forest functional level, but you can set it to a value that is equal to or higher than the forest functional level.