I would say "yes", given that Superliners run on it. This service is Silver Leaf, though, which is usually a single level car with wrap-around windows, like VIA's Panorama cars, if you're familiar.
I'm not a hundred percent sure on the Gold Leaf cars to be honest. A Superliner is 16'2", and the Colorado Railcar UltraDomes are 17'4" tall. So a full foot and two inches according to my records. Now they might be able to fit. That is going to be a doozy trying to deadhead down from Canada trying to avoid low clearances.
The Silver Leaf will clear without an issue which is a former CN CC&F Coach that they converted. Originally those cars were the Red Leaf service which was the cheapest service offered till they decided that they did not want to offer the basic coach accommodations any more. So they converted a large batch over to Silver Leaf and quietly discontinued the Red Leaf product.
This expansion feels a bit half baked though. It seams to me they are going to lose some customers because no one knows what Moab, Utah is unless you google it and find out its home of Arches National Park. But they aren't including any sort of transfer from Moab to the outside world. Moab has a few shuttles that go to the outside world ran by three companies Red Rock Express, Road Runner Shuttle, and Porcupine Shuttle (Grand Junction only). And honestly all three have really crappy websites that are either lacking details or horribly laid out.
Next problem I have with their operation is that they have now launched a product and want someone to place a $25 deposit with them to reserve a spot. That I have no problem with. But when I click on a tour to get more information it goes straight to the deposit page. It doesn't tell me what days they are running, or what amenities might be included, what Gold Leaf costs. If I am going to launch a product like this I would want to have as much as information ready prior to the launch. Now Rocky Mountaineer is lucky that they have very good brand awareness and is well known. But this new project of theirs still leaves me with more questions about what they are planning to operate.
It's not been a large secret that their ridership in Canada has gone down in recent years and I think that's because they have eliminated Red Leaf service which was the cheapest service. I believe it was eliminated in the guise of expanding the Silver Leaf product which was a mid tier product between Red and Gold Leaf.
Their main market is the retiree market which can be very price conscious so I would make the assumption that the cutting of Red Leaf might be the reason ridership has gone down. And for those who would travel Gold Leaf I don't see why you would pay that price. For $1,000 more per person you can ride the Royal Canadian Pacific which has half the capacity of one the Gold Leaf cars on the entire train vs. Rocky which runs up to four or five Gold Leaf coaches in a consist. Its a more personal experience on the exact same routes, still runs daytime only like Rocky, includes off train tours of the various National Parks and cities. They also run on far more scenic lines such as Crowsnest Pass. A far better train at just about the same price, with far better service.
Couple this with the fact the Canadian border will probably be closed for a significant part of next year so there won't be any Americans or foreigners riding the train that almost exclusively markets and accommodates to foreigners. Canadians don't tend to ride the service. The people who have ridden their trains with the money to re-ride I've heard don't want to keep riding the same routes which makes sense. They might be a business in trouble in a decade. So I think they needed to open the new service in order to survive, and it makes sense why they are expanding. But it appears to be only a half baked plan.
I think a better route for them would have been Seattle-Spokane-East Glacier Park. It's closer to their maintenance base, it is equally scenic, and Amtrak runs a significant chunk after dark. When you look at their trains in Canada VIA runs along the same route Jasper-Vancouver. But VIA runs over large portions of that overnight. So the only way to have it all in daylight is Rocky Mountaineer. And the fact they could connect the two trains by keeping the Coastal Passage open.