I think you're confused as to what constitutes "a TTL system". Triggers merely relay the information from the camera to the flash. Whether you're using an AirRemote or a PocketWizard, if you're using Nikon's iTTL system, then you're getting iTTL information and calculations--it's still the same "TTL system" and the same exposure calculation is happening in the camera.
Because TTL systems are proprietary technology, how that exposure calculation is made is generally unknown, so Canon's eTTL may not be exactly the same as Nikon's iTTL, or Pentax's P-TTL, or any other maker's TTL system, so your question in a sense is relatively unanswerable. You could try measuring results to see, but that doesn't necessarily guarantee consistency.
In fact, TTL is not about shot-to-shot consistency. TTL is about speed. The basic function is that the camera tells the flash to throw out a "preflash" burst at a known power-level/brightness. This preflash is metered, and based on the results of the metering, the flash power is then automatically adjusted for the main burst.
Because this is meter-based exposure setting, just like all the other auto-exposure functions in the camera, the exposure will change based upon the scene's metering changing. And this is why most professional studio shooters shun it and prefer M mode on their lights. Just as you use aperture-priority for speed/convenience, you use TTL for speed/convenience, and whether it's the camera's shooting mode or the flash's power mode, you use M mode for precision and consistency shot-to-shot.
TTL is more useful for the on-camera flash photographer who is shooting an event and having to move rapidly in and out of different lighting conditions, who has to capture specific moments in a reactive way (a kiss, a wave, an unexpected "moment"), where split seconds count, and perhaps precision of flash exposure is of less importance to "getting the shot".