Atom package that provides a short cut (CMD+CTRL+P on Mac, CMD+ALT+P on Win) to call plantuml from any editor window that displays some text content. Uses saved content of Texteditor to generate not only a preview but also some linkable file. ExtOnly tested locally on a OSX so far.
Answer: Did You Launch Atom Using The Shell Command?
The most common reason is that atom uses a different PATH than you see in terminal. In the version Atom uses PlantUml might not been included on OS X is due to the way OS X launches processes. When you launch Atom via processes created by launchd (e.g. using Finder, the Dock, or Spotlight) it likely will not have access to your $PATH if you set it in your shell initialization files (e.g. .bash_profile, .bashrc, .zshrc, etc).
Either launch Atom via your shell – using the Atom Shell Commands – then Atom should inherit your environment. Alternatively, try one of the suggestions at http://apple.stackexchange.com/a/87283 to set the PATH for processes launched by launchd (and their children, which will include Atom). An option to set plantuml explicitly
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.