Hi Shane,
thank you for finding Jodd interesting - we really want it to be lightweight :)
Regarding GAE - of course that you may use it! There are some util classes that can not be used, but only few of them, and they are in separated classes, so you will not notice. Besides that, most of the things works just fine.
And we have a working example:) Here is the repo of simple examle:
and here is the application (if you experience lag for the first access, is because GAE needs to 'activate' it):
Also, I know people are using Jodd in their projects and they haven't report any issues so far - but if you stumble on something, please let me know so we can fix that asap:)
Enjoy!