Hi Roseus,
I don’t grow any moss roses but do have a bunch of rugosa seedlings and the seedlings in your pictures definitely seem to have something extra. That’s a cool cross by the way!
They look very young. Perhaps allow them to mature some more so it becomes more apparent? In the below thread they discussed the inheritance of mossiness. Some posters seem to say mossiness can increase over time. Unfortunately all the photo links are dead, but there is reference to an article that you might be able to find on the topic.
I hope someone more knowledgeable about mosses can comment.