I don't know about the blackberry leaves, but rose leaves are good tortoises food. The problem is that almost everyone treats their roses with all sorts of chemicals to stop fungus, aphids and other rose problems. Just make sure the rose leaves your are feeding don't have any systemic pesticides.
I have blackberry in my yard. I think I'll do some research into it and if it is in fact a good green to feed, I'll report back here. that'd be another thing to add variety. The more the better.
They are fine in moderation. They are from the rose family, in fact. If you look, you'll see a similarity in the leaves and the flowers look like the five petaled flower on a wild or "single" rose.