Yes Redbox does allow you to stream movies on demand from your Tablet, Computer, or even a Roku Box.
Redbox has a Roku Channel that you can install on your Roku streaming player to stream movies with but it requires a subscription.
So you don't have to go to the Redbox Kiosk to rent movies but instead if you have a good internet connection you can stream the Redbox movies direct to your computer or Television.