Yes and it is frowned upon. It is best to maintain a pure species. BTW, N2Torts has a couple leopards and sulcatas hybrids. Here is a thread you can see them http://www.tortoiseforum.org/thread-58551.html#axzz2AcKXQi8J
They are beautiful, but should not be purposely bred.
Some species can and have been interbred. It is up for debate whether or not they should be purposely crossed. There are a few threads on the ethics of interbreeding in the debate section. I recommend checking them out. Very interesting reads.
Several different tortoise species and turtle species can successfully produce hybrid offspring with one another. I have hybrids and I plan to produce more for myself and for others who wish to have and observe them.
I have heard accounts of Russian x Hermann's, but I have never seen photographic evidence of that particular cross. Until I see it, that will be suspect.
There are many Greek x marginated accounts. Some with photographs.
There have been red foot x radiated offspring, leopard x sulcata offspring, and elongata x other Indotestudo offspring.
Yellow foot x red foot has been difficult to confirm. Usually a lot of these are speculation due to coloration aberrations, but scale arrangement would be a much smarter approach and more reliable. Likewise, it is easier to believe when you have virgin exposures to animals of the other species and no opposite sex contact history within the individuals of either species suspected to be interbreeding. These animals can retain sperm for years, throwing folks off.
There are other crosses that may be successful, but I will release that information if and when I am so inclined after gathering more information.