Yes as Dan said I use both. I use the common name when speaking to my friends etc and I call them Radiata to my breeder as that is what he calls them. So both are correct.
I just always feel a bit wierd saying Radiata to my friends, when I told my husband that I was going to get some radiata tortoises he had all sorts of images going through his head about flat retangular corrugated tortoises emitting vast amounts of heat. He looked puzzled for about 15 mins until he finally asked me why I would want a tortoise that looks like a radiator!!!!
Whether you are using sulcata as in the scientific name G. sulcata or the common name, sulcata also serves as the plural. However, using the common name African Spur-Thigh Tortoise, would be " " tortoises.