I dont have personal experience with Dolgo as a rootstock, I did find a commercial nursery that does offer it as a rootstock on some trees as of late. They were sold out of many varieties and actual rootstock, sales rep I talked to said that there has been a shortage of Dolgo rootstock for the last couple of years. The new rage for that catergory of rootstock is the variety "Sprout Free". What in particular were you wanting to find out about grafting onto Dolgo?