The only thing that can record from the antenna is a flash drive plugged into the USB port and that's just for pausing and rewinding live TV. It's hardly a DVR. You'd need something like a Tablo to record OTA channels. I wasn't aware there was anything that can pick up the Tablo recordings and I can't find any mention of Stremium and Tablo, but Tablo has an app for Roku devices.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee.