More recently, jazzdev released a version of Jarc that implemented Rainbow's style of JVM access in addition to the Jarc style (http://arclanguage.org/item?id=12684). I cover a lot of corner cases in jvm.arc using reflection, and some of those could probably be implemented in a more direct style now.
One thing to note: Jarc and Rainbow each have their own policies for automatically converting between Arc values and java.util.Maps and such. This is convenient in practice, but it may make some corner-case things impossible without writing custom code in another JVM language like Java. For instance, if a single utility (say, a JSON parser) can return either java.lang.Boolean.FALSE or null, Arc will probably see nil in both cases.
Oh, now that we're talking about it, I seem to remember there's some kind of issue where Jarc allows regular function calls on symbols but 'apply on a symbol doesn't work. So how about (apply 'getTime (list:new java.util.Date))?