Sure, and my team uses Spec at component boundaries to define APIs for that reason. I actually prefer this approach to static typing because it makes it possible to add a specification at the level where it provides the most value, and it's much easier to express semantic constraints using this approach.

It does take more discipline to work with a dynamic language, but once you develop a process then it can be very effective. It's also worth noting that immutable by default plays a huge role here. With Clojure it's natural to create truly isolated components while it takes a lot more discipline in an imperative language where things are passed by reference creating implicit coupling.