As a Ruby ops programmer who came to Rails via Chef I had no exposure to Sandi Metz or any of the other Ruby OO thinkers. However, several years later, now that I have read and integrated the ideas in POODR to my work, I highly recommend it.

Besides Sandi Metz, another Rubyist that I rate highly for delivering clear ideas about design is Avdi Grimm. His RubyTapas series quite radically changed my approach to building applications in Ruby.

Observe that programming in Rails doesn't intrinsically require an OO mindset. But when I reached the limits of the framework, knowing a thing or two about building rich OO domain models served me very well and helped avoid anti-patterns.