I haven't played with the proxy stuff, but Remoting has nothing to do with the system properties - if they're set, they should be picked up when the HttpURLConnection is created. In other words, as far as I can tell, there's nothing in Remoting to break with respect to proxy specification by system properties. There's a discussion here: http://java.sun.com/javase/6/docs/technotes/guides/net/proxies.html. It's for jdk 6, but the system properties go back to jdk 1.4
As far as setting the "http.proxyHost" and "http.proxyPort" parameters in the InvokerLocator, well, there isn't a way to do it as of now. I can think of two reasons:
(1) it's really a client specific issue, not relevant to the server, and
(2) a new HttpURLConnection is created with each invocation, so it's natural to grab the parameters from the metadata map passed to the invocation.
Nonetheless, in a context like the Application Server, where most configuration gets downloaded from the server, I can see why you might want to be able to configure these properties in the InvokerLocator. If you want to create a JIRA issue, I'll make it possible.
By the way, Remoting 2 is more or less in maintenance mode now, so I won't be doing much new development. But for you ... :)