No. Like I said, SimHub can run like overlay, so "on top" of your game. For example here I have the radar widget running on top of Raceroom (plus my pedal/FFB widget on the side that's also made via SimHub):
(What you see in the video is strictly speaking composited in OBS while recording and I was actually running the radar on my phone instead of on the screen like that, but the layout mimics a setup I sometimes use and you can do the exact same thing on your screen, provided you run the game in borderless or regular window and not in fullscreen. Which has some advantages and some drawbacks.)
But you can also run dashboards/widgets on a second monitor, on a phone/tablet or even on a dedicated display, that's also true.