im ie stage 2 with catless dp. i asked them the same questions and got similar response. They told me they don't change anything that would disrupt getting the car smogged or anything emissions related. How ever my car has not thrown a cel with over 5k miles on the tune.When you do, can you ask your mechanic if he sees full 02 sensor readiness with your setup?
Im considering going from IE stage 1 to full stage 2 since it would be only a 100 bucks for the upgrade tune. It seems there are a lot of EQT advocates here and that sounds great but it would be a big cost differential now for me compared to the upgrade tune, plus they started having E30 tunes too. Could aways go that route if I don't like or have issues with the IE tune.
When I asked IE about spacers and DP's they were understandably a bit coy with their response since I believe there is some regulatory pressure on the DP manufacturers these days. There response was the "DP is for off road only, they do not remove 02 codes" and "the best way to achieve readiness is to install the stock DP." So to me this sounds like the IE stage 2 tune is not disabling the 02 sensor (like a test-pipe file), but is a bit unclear if it will achieve readiness.