Giovanni di Buiamonte was a Florentine nobleman who lived in the late 13th century around the time of Giotto and Dante.
The inner ring of the Seventh Circle is a burning hot desert with a continual rain of fire.
Vitaliano di Iacopo Vitaliani, along with Giovanni, are the only usurious sinners to be referred to by name.
However, around the necks of the other usurious sinners are found purses emblazoned with their family coat of arms.
This, and a bit of research into Dante's time-period, make it possible to identify who the suffering sinners are meant to be.