Does Canon ETTL work when...?

I have a Canon 5D II and two Canon 580 EX flashes. I've replaced the feet on the 580EXs with ones that have a mini jack sync port from FlashZebra.com (hardest part was unscrewing the screws from the feet.)

If I purchase a NPT-04 flash trigger set, place one 580 EX on the 5D II's hot shoe, hook the NPT-04 transmitter into the camera's X synchronous port using the supplied synchro-cord, then place a NPT-04 receiver on the other 580 EX flash via hot shoe, will ETTL on the 580 EX that's on the camera's hot shoe work in this scenario if I have its mode set to ETTL?

The NPT-04 transmitter can sit on the hot shoe, but is there a reason not to use it with the camera's X synchronous port and have a flash in the camera's hot shoe?

I realize that the flashes that are using NPT-04 receivers will be on manual, I just don't know about the flash in the camera's hot shoe. I can't think of a reason it won't, but I may be missing something.

I found this about the RF-602. I imagine it applies to the NPT-04.

http://dpanswers.com/c​ontent/radio_flash.php
"The RF-602 transmitter do not provide a pass-through hot-shoe. You can, however achieve the same effect by putting the flash on camera and connecting the RF-602 transmitter to the PC-socket via cable."