Bitcoin built with a newer Berkeley Database incompatible with a older wallet? Is a Bitcoin client built with a newer Berkeley Database incompatible with a wallet file from a older client? Or is it that a wallet made from a newer Berkeley Database not compatible with an older client?   

EDIT: What I'm trying to figure out... If I have a wallet from years ago and I import it into a newer client that was built with a different Berkeley database unknowingly would I have any issues?
You can always open a wallet.dat file created with an older BDB using software using a newer BDB. However, when doing so, the file will be upgraded and not be compatible anymore with the older BDB version that created it. This is even the case for minor version upgrades (4.7 vs 4.8 for example).

Bitcoin Core release binaries have used BDB 4.8 since release 0.4 (September 2011), but self-compiled versions or versions shipped with Linux distributions may use other BDB versions.