Trustees are taking the short sale incentives for the benefit of the creditors when a person abandons their homestead claim. Although it is probably premature to have a definite answer to this question, if you claimed a homestead exemption, I would argue that the short sale incentive is linked to your homestead.
You might as well tell the trustee about this sale, as s/he will find out about the sale from others if you don't speak up.
Hope this perspective helps!
I would contact your bankruptcy lawyer and discuss with him or her the possibility of filing a Motion for Abandonment. If the property has no equity then the trustee may be willing to abandon their interest in it. If not, then the property is not yours to sell.
If the trustee has already abandoned the property then you can argue it is no longer property of the estate nor is the incentive check.
This answer does not create an attorney client relationship between you and I. I am not your attorney unless we both sign a written contract that describes our relationship and terms of the representation. Any information provided to you here is not a substitute for the advice you need to pursue any legal matter. I advise you to retain the services of a local attorney before taking any legal action in this matter.