Yes, whenever pollen grows down into the plant ovary a genetic lottery occurs. Even a self crossing of a plant has a chance of producing a plant with a mutation or even some extra chromosomes. Mericloning avoids some, but not all, of the genetic adventure. I have selfing crosses of both trianae ‘Cashen’s’ and percivaliana ‘Summit’ and they are each different from the wonderful divisions that southernbelle has. I would have preferred a mericlone of ‘Cashen’s’ and ‘Summit’ but I was not able to find one years ago when I was looking. So, if you really love a particular Cattleya the pecking order should be (1) a virus-free division of the original plant, (2) a virus-free mericlone of an original plant, and (3) a selfing cross of an original plant. If a virus infected plant is self crossed with meticulous technique throughout the whole process, it is possible to end up with a virus free seedling, but it is likely to be at least a little different from the original parent and I would probably test for virus for several years of growth.