Kind of but many streams are not accepted by plex, if you use basic http transport streams you should be ok but there are limitations and issues with it being a flawless experience. There is a plugin here for example
https://github.com/Cigaras/IPTV.bundle Most should be fine but a few setups may have issues, especially for those who just maybe bought a box and have no technical skills.
Personally i assume they will clamp down harder as they made a big choice, stay favourable to pirates or go legit, they chose legit. So knowing that i have to assume they will do whatever makes the .us government happy on a whim. That would see shutting down all apps that lend themselves to piracy on the roku platform as perfectly possible a situation.