Generally speaking, a reboot is only required if the system asks you to do so. Sometimes the setup kit asks you to stop some services in order to avoid having to reboot your machine. Concerning PI Coresight specifically, I have recently upgraded this product from version 2013 to 2014 without the need to reboot the machine. But again, consider what the setup kit asks you to do since it installs/upgrades other products as well.
Hope it helps!