Unless you are going to run an after market electronic dash you will still need the stock ecu in there for that reason as it feeds the information to the standard dash. Unless someone is going to spend the time wiring in all the dash out controls etc.
The problem with the standard throttle is it is delayed giving full open throttle. That is helped by doing the brake cut mod, but there is still delays.
I am not 100% sure on the haltech and so on, but my guess is unless you are going to pay for a massive full re wire of the car and then have them program in the cable throttle to run straight off the haltech that they will still be using the stock ecu to control the electronic throttle.
By going cable throttle as I have done and they recommended it would fix this problem.