As for the uninstallable part, well, there are ways to make it difficult to uninstall, but if those delivery guys are a bit techie they'll find a way - they have root access after all. If those guys have no idea what xterm is, simple cron execution is more than enough to 'conceal' it. However, I wouldn't worry about it anyways - if they don't want to be tracked they can always disable internet connection on the device, or even turn off all the radios (airplane mode) and then all your efforts are in vain.