I think all SAS math programming packages do not provide hessian value at optimality. SAS says will provide it in optmodel package.

You may re-write your problem in proc nlmixed that does MLE. Or you can use SAS IML to evalueate/calculate Hessian at  optimality and calculate other statistics.

Here is IML call for 1st. 2nd order derivatives.
CALL NLPFDD(logl,grad,hess,"lik",xr);


logl= function value at optimal point ;
grad=1st. order derivatives -returned value (vector)
hess=2nd. order derivatives -returned value ( matrix)
"lik" = your defined likelihood function
xr  = optimal estimation (vector)