Washington was a curious choice, perhaps inspired by then President Tucker's modern liberalism. You see, Daniel Webster is most famous as a great orator, fierce lawyer, and as a U.S. Senator who could get bill passed. Less talked about is his infamy for rousing the votes needed to pass the Fugitive Slave Act in 1850. That law forced federal officers to capture and return runaway enslaved people in Northern States and made it a crime to assist those enslaved persons whom had fled to the North. As you can imagine, the law was hated in the North, but Webster, seeking to preserve the Union, saw fit to give the speech that persuaded enough Senators to pass the bill. So here is Tucker, celebrating Webster's legacy by conferring an honorary doctorate on the most well-known civil rights leader in the United States who had been born into slavery. He must have known exactly what he was doing--a moment of symbolic resistance among the celebrations.
To see the letter Washington wrote to Tucker to accept the invitation to the Centennial, ask for MS 901557.1. The D has a great account of the festivities in the September 27th, 1901 issue on our reference shelves.