Is it permissible to use a duplex sump pump control panel to control two receptacles instead of direct connections to the sump pumps? (the pumps are 120V fractional HP)

As an inspector, my answer would be yes, provided the controller meets the requirements of the code for a motor controller. I have seen a controller probably not unlike the unit you are talking about. Some of these controllers are for single pumps and some are duplex. In the installations I routinely inspect the controllers are located within site of the point where the pumps are submerged and the controllers have an integral switch which serves as the motor disconnect.

In this case the pumps are in a sort of area way with the control panel next to the access. There is a disconnect before (and in sight of) the controller which would disconnect all the power. The receptacles would act as the pump disconnects (if the main disconnect, which is close, is not in sight of them).