So, I eventually got around to looking into it further and I suspect this isn't news to most people, but maybe it'll help someone trying to find similar answers:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<string>Symbol List: Method</string>
I kinda fumbled my way through, but hopefully jps will add a better, or more complete set, of Ruby Symbol List tmPreferences file to an upcoming build.