Technically I think Dyckias are not succulent. Their lifestyle is very much the same and I love them because they bring on the hummingbirds, but you might want to check on that.
In my opinion the so-called Purple Crest Aeonium is kind of a made up name for a plant that already had a great name to start with: Aeonium "Zwartkop". That spelling may look weird, but it's a Dutch word (the plant has Dutch origins) and it's the exact equivalent of Schwarzkopf in German, with the most appropriate literal meaning Black Head if you were to translate to English. Random trivia burst there for you but it does have to do with the character of the plant and its history.
To your questions:
Maybe the best way to go at which plants are round leaved would be to identify which ones are not. I think round is sort of a default for some groups of succulents (it is the most efficient way mathematically to store water). Some exceptions would be plants with lots of spines (for example agaves) or sharp angles (Crassula perforata), or more fibrous than succulent (Yuccas). Leaves that are long or pointy (for example Echeverias). And there are lots of succulents that don't make leaves at all, and they look round because the stem is round (like many cacti), so you would exclude those from the group as well, or consider expanding it, so there is no confusion. Some of my favorite round-leaved succulents are New World plants: Pachyphytum, some Graptopetalums, some Sedums. Also the common jade and Elephant bush (P. afra). Senecio rowleyanus (string of pearls) is the ultimate round-leafed plant because they are literally spherical.
What is a rosette? You should probably look that up but my general use of the word describes pretty much any group of leaves around a stem. The spacing may be tight or loose. Echeverias and their kin all make rosettes (Pachyveria is actually a hybrid between Pachyphytum and Echeveria). Some rosettes are not real obvious as such, for example my avatar (Aloe plicatilis) which makes a flat rosette, or some trailing plants (Sedum burrito) which have an extended tail, or some rosettes which can pack together in clumps and be hard to resolve, like Dudleya attenuata.
In addition to the "living stones" (Lithops) and "split rocks" (Pleiospilos) of Southern Africa, I suppose there are probably a bunch of cacti which use mimicry to blend in with the landscape. Some are more camouflaged than rock-like (check out pictures of Ariocarpus in habitat). To my eyes the globose Euphorbias (symmetrica, obesa, valida) tend to stand out more than blend in because of their near-perfect geometry, but they most definitely would be able to blend in otherwise with their color and texture.