Tasker can hide Android Oreo’s ‘App is running in the background’ notifications, root not required
One of Android Oreo's many new features is a persistent notification for each app that runs in the background. While this is certainly helpful for the average person, it can get old quick for power users that frequently run applications like Tasker and LastPass. If the messages really get on your nerves, you can now use Tasker and the Notification Listener plugin to hide them.
You can view the whole instruction guide at XDA, but it involves installing both Tasker and Notification Listener (linked at the bottom of this post) and importing a Tasker profile. Once that's done, you can either trigger the task manually to hide the notifications, or set the trigger event to "Monitor Start" to hide them automatically. Root is not required.
If you're wondering how this works, it's actually quite simple. The Tasker profile just snoozes the notifications (which is another Android Oreo feature) for an incredibly long time. 317098 years, to be exact. The profile actually snoozes all notifications from the Android System process, but you don't have to worry about missing anything important, because the only notification it provides is the one we're trying to hide.
It would be nice if Google provided an option to hide the messages, like in the System UI Tuner or Developer Options. At the very least, I hope this workaround isn't disabled in a future Android update.