Tesco, that will be detected by any level of non passive EM scanning, and it will block only level 1 of passive EM scanning. A level 1 gravitic scanner, for example, can detect such a ship. You do not need all levels of cloaking on a component to get some cloaking (such as stealth armor), but you have to be wary of other scanning types when setting it all up.
Check out P&N PBW Version for an example of a system where the cloaking abilities are separated into different components.