I don't see a problem with requiring Rails experience. It depends on the job of course. If I don't mind a slow ramp up and want someone right for the job that might last a few years then I don't care. If I have some complicated technical issues I need fixed quickly, I want someone that can jump in and go right away.
Particularly with Rails where it's convention over configuration, knowing the conventions is a great headstart.
Then you probably need consultant if it is only for a specific issue. Otherwise once this is solved you got bored to death employee, with skill set for which you are overpaying and under-utilizing.
Unless you need language guru, the languages known don't matter much. If someone can write a LISP interpreter in Haskell for 2 days I would hire her for a Java position even if she doesn't know what a loop is.
Particularly with Rails where it's convention over configuration, knowing the conventions is a great headstart.