I know it is not in the base package. I am pretty sure it is not in the News Pack, but I don't know if any other add-on includes it. Many of the cheaper channels that are included in Welcome Pack are available with the Latino Bonus Pack. If there is no way to add RT to Flex Pack, I would recommend Welcome Pack, which definitely includes it.
Yes, RT is available for free on the Roku. RT has their own app along with RT doc channel as well as RT in Spanish. Tons of free International news channels on the Roku, Turkey, France, UK, Germany, Russia, UAE, Ireland, Israel, Iran, India, Saudi Arabia, Japan, South Korea, and China. There may be others too. Roku is great.