I believe this is just a misconception.
There is nothing in the tcm code that requires the engine to be running a 58x reluctor. Since everything they get is transmitted over the canbus they just need at a minimum to receive RPM, Pedal Position & engine torgue figure.
All of which the E40 transmit. Remember they are sending the exact same info to the T42 controller for the 4 speed for it shift.
There are a couple reasons why I don't think an E40 will work.
1) The first year of the C6 Corvette in 2005 was sold with the 4L65 automatic and not the 6L80, guess it wasn't ready yet. In that first year, they used the E40 ECM. In 2006 they switched to the E38 and started using the 6L80. I can't see why Chevy would absorb the cost of redesigning wiring harnesses and switching ECMs if they didn't have to.
2) 2005 Pontiac GTOs were the first ones to use the E40 ECM. In 2006, there was a hardware revision to the E40 and a new OS from the 2005 version. We know in the US that you can't use a 2006 ECM in a 2005 GTO, and vice versa, because they switched pin assignments around. If they did a hardware and software update you would think they would include the ability to talk to a 6L80 and therefore Chevy would have kept using it.
So maybe it can be made to work, but for whatever reason, GM didn't think it was worth doing.