An OS X upgrade (to OS X 10.6.8) should not disrupt your existing application environment, though you will still want to have a full backup or three of your environment; via Time Machine or some other mechanism used for creating a complete backup of your existing OS X storage.
If you're using OS X Server or the server tools and upgrading to 10.7 or 10.8 (if that's supported on your Mac), then there are other considerations; these are among the tools that do have OS X version dependencies. There may well be other tools you have that are version-specific, too.
Even outside of the context of any upgrade, you will want to have these disk backups, as systems and disks can and do fail, and disks can be corrupted.
If the above does not address your question, please post up any details that I may have missed or misunderstood about your question and your OS X upgrade.