You don't need to go through Roku's support folks to set up an account without a credit card. I didn't have a card attached to my account until recently, and I definitely didn't need one initially. It's been a while since I've seen the setup screens, but when you set up the box, it does prompt you to enter a credit card for purchases... but there's an option to skip it right on the screen. You can just continue without one.
That is only true for previously set up accounts. New accounts do not have the "skip" button displayed. That is unless it has been added within the last few weeks and I doubt that it has.
A long time ago, like two years or more, the CC was not required but it has been required for some time and the only way to skip it was to contact support.