Now I could be wrong, but so far, having seen the products of my varied flock, it seems to me that a flat or really any comb structure/ shape, that is Not a single comb, is dominant over the single comb. So my guess is you will have Rose comb Orpington chicks. More frost resistant! YAY!
I have had chickens for a year now. Currently I have 19 birds. 1 Lavender and 2 Buff, Orpingtons, 2 Buff Chanteclers, 1 Barnevelder, 1Whiting True Blue, 2 Mistral Gris (a Canadian meat bird, though mine are elevated to egg laying status), 2 Russian Orloffs and 2 Silver Hamburgs. I must not...
I have heard Buff Orpingtons CAN have rose combs. Though its not usual. So can Rhode Island Reds. This too is not typical. so they both can have rose combs and still be pure breeds.