RubyMine doesn't support RubyMotion or the iOS SDKs now, but they're considering it (cf. http://devnet.jetbrains.net/message/5458781#5458781). You can vote up the feature here:

http://youtrack.jetbrains.com/issue/RUBY-11039#tab=Comments

I would look at the autocomplete scripts/library, see how the metadata is handled there, then see if the autocomplete data in XCode can be hooked up.