What your asking is very difficult to answer as it depends on the hardware/brand.
Doorbird cameras will refuse to work when the app has control for example, but other camera brands I have working 100% in home assistant and openhab at the same time.
I usually power off the HA box as you also can’t rule out that some devices may crash more often it they are busy answering multiple platforms.
Lastly the concept I prefer to use is for devices to operate in stand alone mode and only use openHAB to over ride the hardware when needed. This way if I ever need to rebuild I don’t have an entire house not working for days as all devices keep working with openHAB turned off.
Multiple approaches, which I prefer to decentralise and distribute the intelligence if I get the chance/choice.