That is really odd. I can't imagine why it doesn't accept keyboard input.
Last night we released a new launcher for Mac, so you might try to download and reinstall. If that doesn't work, you can try running Spine using your system Java from Terminal:
java -jar /Applications/Spine/Spine.app/Contents/MacOS/launcher/launcher-full.jar
This requires you have Java installed. You can try different Java version, eg Java 7 or 8 by Oracle.