I have had a Roku channel that feeds from Kaltura since 2013. There is a new Roku service for developers now, called "Direct Publisher" that makes it a breeze to setup the Roku Channel part now. Just walk through a few "wizard" steps and viola. The trick is getting the feed setup on the Kaltura end. This part requires some XSLT expertise (the default Roku Feed included with Kaltura, although a great place to start, has never worked for me in it's default form), and some time to get it tested within the Roku setup. The "Direct Publisher" will accept two different kinds of feeds, JSON and MRSS. I've created both (ok,ok...I've modified someone else's) and although I can get the JSON output tested correctly by cutting and pasting it into almost every JSON checker on the web, it never tests correctly when coming directly from the Kaltura feed (I'm pretty sure it due to the Kaltura custom feed failing to include the JSON application type.) So, I am using the MRSS type to feed my channel. It just means I can't send as much detailed data to the channel.
Long story short, Kaltura is a great way to provide content to a Roku channel, it just takes a bit of time and possibly a little sacrifice when it comes to the detail level of your channel items