No. The Flex vent may sag creating a downward section of exhaust flow. During operation, condensate may collect in this section (create a condensate trap) and cause issues for the unit/vent. To remedy this situation, remove the coupler from the flex vent and trim off the excess. In removing the coupler, take care to not use excessive force removing the coupling (see example below).
Condensate
Liquid water that forms when the water vapor, developed as a product of combustion, contained in exhaust gases cools enough to change into a liquid.