Sorry, I initially wrote 'interfaces as in OOP' to distinguish them from module interfaces, but had 'ad-hoc polymorphism' in mind. 'interfaces' is much too overloaded of a term.
Ocaml has no ad-hoc polymorphism but you can use parametrised modules to write generic code which you will have to specialise at some point. That brings you ninety percents of the way in term of what ad-hoc polymorphism is used for. It's more cumbersome but I prefer it to the complexity involved by what Scala does for exemple.
The OCaml object system is still parametric polymorphism (trying to pass itself as subtyping polymorphism through row variables) rather than ad-hoc polymorphism: there are still no functions that only work on a finite subset of types. In other words, a function may work on any objects that has a method `m`, but you cannot have the same method that has different implementation for `int` and `float`.
It uses structural typing not ad-hoc polymorphism. Plus it’s rarely used and it used to give hard to parse error messages when you made type mistakes. I don’t really see it as an adequate replacement for ad-hoc polymorphism.
