I’m not a UML-guy myself, but have been on the end of a few UML presentations of new systems/processes, etc. Generally the problem with UML is that it can support definition to a very low-level of detail, but does not always “bring the processes to life” for normal business users, who have no UML training. It also captures some of the requirements in the syntax of the method, not just the content, which can be lost on non-UML folks.
Often I suggest that analysts continue their UML work (it will be very useful for software builds and detailed process implementation, defining training requirements, etc), but also work on some PowerPoint based “use cases” or “scenarios” that capture a single moment, or customer journey, or user experience. If the project has a software build component, then it can be useful to mock up some screen shots (even if they are also in PowerPoint!) – many business users find it easier to understand a system by following a sequence of screens.