replace native samsung galaxy s3 email app for gmail app? Is it possible to disable the native email application that comes with the samsung galaxy s3? I feel that the UI is inferior to the gmail app.

If so would this require rooting into my phone?
Summary of comments, as requested by the OP:

If your device is running Android 4.x, you can simply go to Settings &rarr; Applications &rarr; Manage Applications, scroll to the app, oben its entry, and hit the "Disable" button -- et voila, it's "gone", and will no longer appear in any other place. If you need it again at a later point, it will still be at the end of the list, so you can enable it again.

Note though, that some manufacturers / ROM builders decided to preventing some apps from being disabled. Nothing you can do in that case without root. If you rooted your device, on the other hand, apps like e.g. Titanium Backup ★ root would let you freeze those apps as well.

Note also GAThrawn's comment: If you don't configure the email app, it won't run. Some homescreen replacements (aka "launchers") allow you to hide unwanted apps from the app drawer (e.g. GO Launcher EX), so you at least can ban them in some way.