Receiver, ESC need isolation?
ESCs expect the signal to be 4.8V. It's only the power (motor) battery that is normally a higher voltage. The BEC circuit reduces it to 5V, that's its purpose. Removing the red wire should work.
However if your ESC has a low voltage cutoff associated with its BEC circuit you may have problems. Most ESCs are not intended to run on as low as 5 cells (6V nominal) so it may keep switching the "motor" (smoke pump in your case) power off because it thinks the battery is getting too low to run the radio. It has no way of knowing that you've disconnected the BEC so it doesn't matter.
Steve