I harvested what little of my own hybrid rose hips I had. On average each contains 3-5 small rose seeds, however I peeled away one hip and inside was one huge seed, it was the size of the rose hip itself just missing the skin! About 3x as large as a normal seed. Does this mean its going to be a huge plant, its a hybrid I created on my own.
I dont' know the answer to your question. But I just filled out a survey for a professor at Texas A&M who is researching hybridization of roses (link sent out by the ARS). He referred to the Rose Hybridizer Association. I saw you question and looked them up thinking they might help you. It turns out they have a forum: http://www.rosehybridizers.org/index.html
You might try logging on and asking there. I would be very interested in finding out what they tell you. I always try to learn something new everyday. And your's may be the something new I get to learn today ☺!