I see from your profile you already have stock fogs installed, are you planning on omitting the fogs altogether to replace with aftermarket? Just cut the connectors and wire up new lights. I've done it. Keep in mind the factory wiring was intended to run the 55watt fogs, many aftermarket lights exceed that. Some have run 100 watt lights (me included) but many would say the risk is not worth it.
If you are trying to supplement your oem fogs with additional lights, then run a separate harness. It's not that hard. If you wanted to you could use the low voltage trigger from the fogs to your new relay to switch the new lights. You could even use a 3way switch to have them on/off/on auto with fogs. I've wired several circuits that way. That answer your question?