Yep, OBS can get audio from your interface, and from other apps. So you could mic up your amp, and use another source (winamp, an ipod plugged into your computer) for the backing tracks. No DAW needed.
Pro Tools would not be able to use this particular method anyway, because ReaStream is VST-only. There might be a Pro Tools way to route audio elsewhere within your computer. I use ASIO Link Pro. Others use Voicemeeter Banana. Mac users use Soundflower.
Anyone with questions on this stuff: just download OBS and try it out for a bit. Then you'll have a better of idea of what else you need to know. I use OBS Studio, but I've heard Streamlabs OBS is better.