Can you climb at Vxse when you cannot at Vyse in a multi-engine aircraft?
I'd recommend reviewing Chart 5-23 from the PA-44 POH - Climb performance one engine operating - gear up for specific numbers based on aircraft weight and atmospherics.



If you're not seeing a positive rate of climb at your best rate of climb, single engine airspeed, then you're not going to see it at the best angle of climb airspeed single engine either.  By definition, Vyse is the best rate of climb that you're going to see on a single engine; any other airspeed, including Vxse, is going to give you a lower rate of climb, or greater rate of descent if a positive rate is not possible.  And attempting to acquire and hold Vxse you're getting close to the reverse side of the power curve, combined with ever decreasing rudder authority, it would be easy to have the aircraft drop below Vmc and depart from controlled flight.