NOPE. Absolutely, positively not.
On an Equinox, the "watertight seal" DOES NOT OCCUR at the handle-to-shaft interface. Take your handle apart and remove it from the shaft, and note that there is NO RUBBER GASKET OR O-RING between the two parts of the handle that fit together around the shaft. The watertight seal occurs farther up inside the handle -- at the door of the battery compartment (there are two rubber o-rings inside the battery door), AND, as I understand it, farther up inside also, where the handle and the control box meet/join. SO -- the handle-to-shaft interface is NOT a "watertight seal." Using an aftermarket carbon-fiber shaft DOES NOT, and CAN NOT, in any way, risk the "water-tightness" of your Equinox. Period. There is no "seal" that occurs at the handle/shaft attachment point, and so there's no way WHATSOEVER for your shaft -- WHATEVER shaft you are using, to be associated with leakage issues.
Steve