Yes, there have been App Store approvals of Rhodes apps. Search the Google Group and you will find posts from authors of apps that have been approved.
I think the most likely causes of rejection will be poor responsiveness and flakey UI (transitions, in particular) due to the use of jQuery Mobile. Surprisingly, JQM is the biggest bottleneck in Rhodes apps. I do not see the Rhodes Ruby core as being any hindrance at all to app performance.
The JQM issues can be worked-around. You don't have to use JQM, and if you do, there are work-arounds to the visual artifacts and performance. One thing you can do is to keep it simple! Don't use transitions. "none" transitions are very fast. Don't use listviews, they are slugs.
I have demonstrated the ability to put a fairly complex page on the screen in Rhodes 50mSec after the user first touches the screen - getting the data from a Rhom database using Property Bag model, and using jQuery Mobile 1.1.1 or 1.2. This would be very hard to distinguish from native. It's doable - just not right out of the box.
if you do, keep your page to device height and either stick with the JQM 1.0.1 that comes with Rhodes or else retrofit the 1.0.1 transitions into newer JQM. Another thing is to use some tricks to avoid the Mobile Safari 400-mSec click delay.
I've written two jQuery Mobile plugins that help:
I've also been helping some clients to get good performance out of jQuery Mobile, both in Rhodes projects and PhoneGap and webapps.
There have been ongoing rejections over database placement in the file system. It is spotty. This needs to be addressed!
I think submissions right now will have a tough time until the iOS 6.0 orientation problem is fixed. For the next few weeks, you will have to be able to make a good case why your app is only suitable for a single orientation.
Here's a little secret: Apple is must less discerning about apps submitted from authors in countries other than the U.S. I suspect the less densely-populated your country, the easier acceptance is. (I have not done any research on this - it's just my personal observation.) I'd also imagine they are more lenient the smaller and more-targeted your audience is. If you are writing the next Twitter or Facebook (or wanna-be), they are going to be very picky.
Thanks for your very thorough answer, including the things that work and those to avoid. It gives me greater confidence that my efforts with Rhodes will pay off. I'll check out the Google Group as you suggested.