no, with most high to mid end gpus they will not work with the igpu and will not hyrbrid crossfire either. Hybrid crossfire only works with lower end cards and i think a 7750 is max and the benefits are not great. If buying a new system go with a better cpu and dedicated gpu or apu only. If u want to use the apu in low power situations or when ur not taxing the dedicated gpu its pointless, as under idle or low use the cpu and gpu will either downclock or something and use less power and produce less heat. Under idle many gpus can use under 10watts, could be less could be more all situational. With power profiles and power savings features on cpus many drop the voltage and clock and can normally lower the cpus tdp under idle.
basically the igpu will disable when a nvidia card is put into the system or anything higher than a 7750, well not disabled but will not hybrid crossfire with the card to gain extra gpu power.
I see no situation where wanting a dedicated gpu and the apu at the same time when not using them for hybrid crossfire. Most normally go with one or the other. Personally i see no gain with hyrbrid crossfire, but i dont and havent ran it at all but seems like a waste as u can get a faster gpu for only slightly a few more dollars.