It was an option on my coach. However, I did not see an option for a spare in the ACE brochure, so it may not be available. You will also want to find out if there is a spot to store it.
Regardless of whether or not you have a spare, you will certainly want to purchase some kind of road service when you buy your RV, either Coach Net, AAA-RV, or others as you will not likely be wanting to change the tire yourself.
So in reality, not having a spare is not as bad as it could be.
True, a spare gets you on the road a bit quicker, But, if you have a non-repairable flat, you may be able to "order" a new tire when you call on the big-rig wrecker to rescue you. Some wreckers may be able to re-mount a new tire in the field, so if you don't have a spare, it might take a bit longer to get back on the road due to having to re-mount a tire.
Or, you can always buy an unmounted tire for a spare, which would be easier to carry (less weight and bulk), and always have one for the wrecker if needed.
The only thing that works on a RV is the owner...