Just a clarification -- remember that when roses are released, their classifications are chosen by the breeders and/or introducers, and that's heavily influenced by how the rose will be marketed. Originally, Grandifloras resulted from crosses between Hybrid Teas and Floribundas, but as breeders look to widen the genepool for health, roses with other ancestry will be thrown in. So just because the "typical" Grandifloras you know don't sucker, don't assume that any rose classed as a Grandiflora won't sucker.
Most roses grown on their own roots will increase in root-mass and send up new canes a bit away from the center over time. Sometimes it's hard to draw the line between "suckering" and simply "widening the clump" because there are roses that are sort of in between, but some sort of spread is almost inevitable given enough time. I had a potted own-root 'Nigrette' (an old Hybrid Tea) for a few years -- I've since planted it at my cemetery project -- and every year, it made one sucker, which I'd pot-up and give away. When I took it out of its pot, I realized that what I thought was one plant had become two, so I separated it and planted each half.
This is why I prefer own-root roses for the garden. I understand that some people exhibit, or want cutting-quality Hybrid Teas for the vase, and so buy plants on vigorous rootstock for that purpose. If something I want will sucker widely, I plan accordingly, and put it where that isn't an issue. If a harsh Winter, disease, damage, or a need to transplant means I have to cut back severely, I know that a healthy root mass is the "heart" of the plant, and new top-growth will reappear.
:-)
~Christopher
