Hello, I use rose hips in one of my xmass beers, I use 1 oz cracked, remove the hair and seeds, add at 15 min left in the boil.
This beer has cinnamon, all spice, nutmeg, orange peels, in it too, so its kinda hard for me to suggest to you exactly how much to use, I cut the rose hips in 1/2 on this, as i felt that 1 oz was just a bit to much with everything else going on in this brew.
For a pronounced rose hp flavor, I would recommend anywhere from 1oz to 2oz at 15 min left in the boil, I think 2 oz will be very up front in your beer, this is my best guess.
I hope this helped, Please let me know how it turns out.
Cheers