I would let them come to room temp, as above, if you have a salty rub on the outside, you won't have to worry about any surface bacteria, and bacteria and other nastys cannot readily penetrate the rib roast, which is why you don't have to cook it to 165 degrees like you do chicken our cook it through like ground burger for food safety.
Do not trim off all the fat cap off the roast (it is going to baste your roast with flavor), you can trim it to a uniform 1/2 inch though. Your fat will begin to render around 130 degrees and continue through your cook. Because it is on the outside you will get some fat dripping, which is a good thing, but it won't all render unless you accidentally cook the fark out of the rib roast. After all, the idea by not putting the roast on cold is that you are getting the rib roast up to med-rare almost all at once. So if you are concerned about drippings getting all in your smoker and making a greasy mess, instead of trimming all the fat cap away, I would instead suggest utilizing a drip pan under your grates below you rib roasts. That's a lot of prime rib. Sounds like it is gonna be a party. Good luck! Post us some pics.
LG BGE-Brinkman Cimmaron-Custom Pull-behind (old grade school boiler)-Weber Kettle-DCS 30"