Why is it that competitive chemical inhibitors will stop binding to an enzyme if there is a build-up of substrates?
Why don't non-competitive inhibitors also stop binding?
A competitive inhibitor binds to the enzyme's active site. We can reverse this inhibition by increasing substrate concentration, as the substrate can essentially "overpower" the effect of the inhibitor by occupying the active site instead, in a way 'forcing' the inhibitor out of the active site (remember that the enzyme in this scenario is specific to both the substrate and the competitive inhibitor).
Non-competitive inhibitors
do also stop binding (I think you may have made a small error in the question
), but this form of inhibition is not considered reversible (within the bounds of the VCE curriculum) because the inhibitor binds to a site OTHER than the active site. This distorts the shape of the enzyme's active site, which means that increasing substrate concentration will have no effect because the substrate cannot bind to the active site.
Can digestive enzymes also be called hydrolytic enzymes? (Or is it best just to refer them as the former?)
All digestive enzymes are hydrolytic (the belong to the class of enzymes known as hydrolases), so that's fine!