Corellium is more for low-level library and kernel debugging and situations where you need control over the boot process, the same kind of thing you'd use qemu for vs. the iOS Simulator in Docker-OSX or AWS Mac instances or whatever. For just running UI tests, AWS Mac instances or Appium/Browserstack/whatever is going to be way cheaper and more practical.

For low level debugging situations using real hardware is impractical or impossible as you need stolen debug probes (or to be part of the super exclusive Apple research program) and/or custom hardware.