Yes, 2008 R2 to 2012 will work, but it can only be used for 1 way, once you make the 2012 instance active (WITH RECOVERY) you will no longer be able to logship back to 2008 R2 (role switching will not be allowed back to make 2008R2 primary).

You cannot put a database into STANDBY mode when crossing version, it has to be in NORECOVERY mode.

If you need the secondary copy to be in STANDBY then primary server will need to be 2012 or secondary server will need to be 2008 R2