I’ve seen this quite a few places. Don’t these two words contradict one another? How would someone who does RoR consider themselves to be a FRONT-END developer?
Seems to me like it’s equivalent to saying JavaScript Server-side Web Developer, unless maybe I’m missing something?
Does seem a bit odd to me, as RoR is a backend language (as far as I understand it).
However, there is such a thing a server-side JS.
They do contradict each other, I’m guessing what their intending is the front-end developer would be someone who produces the GUI (graphical user interface) of the application in preference to the behind the scenes code. Rich internet application frameworks like ruby and python (unlike stuff like PHP and ASP) have an entire industry based on making interfaces for the functioning code within the language (aimed towards the end users experience). 
Maybe they are looking for someone who has a lot of experience using the Prototype JavaScript helpers?
This usually means a person who does all front-end stuff (HTML, CSS) AND implements it as RoR templates (thus the requirement to know RoR).
Rails is an example of the Model-View-Controller framework. As a front end coder you would still need to be pretty proficient in the Controller and View aspects, mostly helper methods.
i am searching for a visual gui for doing drag-and-drop web-page layouts, which generates ruby-on-rails code.
An RoR front-end.