It sounds as though you are looking for a way for your designers to do
full page visual design. Our product, Ruby In Steel Developer, is the
only Ruby IDE that has a full page drag and drop design environment for
Rails. it assembles and translates Rails (Erb) templates into editable
HTML pages. You can drag and drop buttons, text fields etc onto the
pages and apply CSS styling. When you like the design, Ruby In Steel
automatically splits up the HTML pages and translates them back to their
original form as multiple ERb templates (layouts, views, partial).
Some info here:
Moreover, if your designers prefer to use 3rd party tools such as
Dreamweaver, it takes care of exporting your page designs in editable
format (to Dreamweaver, Expression Web or whatever) and importing them
back when the designers have finished.
More info on that here:
Ruby and Rails In Visual Studio