Question: Is there any way to tell whether a particular application running on Mac OSX (10.2+) has some of its memory swapped out (i.e., to one of the `/private/var/vm/swapfile*` files)? And how much?

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Answer: 
The `vmmap PID` command should give you some helpful stats in numbers about a given process.
Open up Activity Monitor in your /Applications/Utilities folder and there is a Virtual Memory column that will tell you this. You can click on the Virtual Memory header to sort by most or least used by application. Also be sure to change My Processes to All Processes, and be aware that one application could have multiple processes. For example the 3rd party application Little Snitch is comprised of "Little Snitch Network Monitor" and "Little Snitch UIAgent."