<p>Ever since the publication of <a href="https://rads.stackoverflow.com/amzn/click/com/0321200683" rel="nofollow noreferrer" rel="nofollow noreferrer">Enterprise Integration Patterns</a> people have been using the notation introduced in that book for documenting asynchronous heterogenous messaging systems.</p>

<p>But our shop is more or less standardized around a proprietary documentation tool that does exclusively UML. Is one of the standard UML diagrams appropriate for documenting asynchronous messaging systems, including transformers, routers et al.? If yes, which one? If not, what would be a killer argument against the tweaking of UML for this purpose?</p>

UML provides a mechanism for extension through
profiles
A profile allows you to specify stereotypes, tagged values, and constraints.
Every stereotype can have an optional stereotype icon.
Perhaps there is an EIP profile for UML you could download?
If not, you can build your own profile if your UML tool supports this, and use the icons available as Visio shapes from
Gregor Hohpe's website
Hope this helps.