Indeed. Monowhips benefit from the extra successes, same as any other weapon. They just don't add STR to damage like most melee weapons do. That's just fine, though, for low STR characters. I like to use them with Pixies, as well as some mages or faces. But you need decent points in the skill and in AGI, or those crit glitches will be coming more often, and that will cut your run real short.