We just published the version 0.2.0
of the OAuth.io Cordova/Phonegap SDK, which fixes the issue with Ionic.
Now you should be able to use the cordova plugin in a ionic app without any trouble, like this:
$ cordova plugin add https://github.com/oauth-io/oauth-phonegap
This version also contains features that were missing from the sdk, like the cache and the unified user info method.
You can get more information about all this on our github page:
https://github.com/oauth-io/oauth-phonegap
Hope this helps :)