Please take a look at this article: http://www.infoq.com/articles/sharma-charts-in-rails.
This will help in integrating FusionCharts in Rails.
As far as I know, you don't need any plug-in to integrate FusionCharts
Angular guage is a part of FusionWidgets v3. You would need to buy a
license, if you already haven't.
To produce the xml for the angular chart, refer to the documentation
There are several FusionCharts Rails related discussions at :
Hope this helps.