I'm a little confused on your response. Do you know for sure that he is buried in that cemetery? If so, the cemetery office should have records of his burial which should give you information. The memorial listed as it is indicates he is buried there to other researchers and that he died in that year. There are no bio notes indicating otherwise to anyone viewing the memorial.
If she is not sure he is buried in that cemetery, the better option there is to have listed him in cemetery unknown with an unknown date of death.
Or, are you just looking for some other proof such as a death certificate to get the exact month and day of his death in 1898?