Viper,
When you boolean the objects together, That will become your surface (the part inside of the buckle goes away) Your new surface is what you see. If you dont boolean them together, then when you bring it into your cam package there will be multiple objects and your letters would be .25 inches all the way to the bottom of the part. You could choose to control this with the cam package though, and since you have fairly flat surfaces, wouldnt want to do it in 3d anyway. You'de want to do it with profiles and pockets and control your depth from there.

There are many ways and it depends on what you want/need or what your cam package is capable of. (Make the solid then extract the edges for the profiling and pocketing)

What are you using to cam the part?

I'll post some examples in a bit!