If the design document you refer to is the design document for a project delivery, and in that design document risks are raised, then those would be drawn into the risk log for the project and managed in the same way as risks raised in any part of the project.
However you appear to have made an assumption that the design document ruling DR out of scope for the solution design is an operational or business risk. That does not automatically follow from the information you have provided. A definition of scope defines what is within the scope of the project (and also out of scope of the project). In this case, stating DR is out of scope of the Design Document merely says that the design document does not cover any elements of DR (and by extension the project itself does not deal with any aspects of DR). That is only a project risk if a goal or objective of the project is to deliver DR (or perhaps it is an infrastructure refresh and the refreshed infrastructure needs to introduce DR or continue to maintain a DR component).
Whether or not it is an operational risk or business risk is irrelevant if it is not in scope of the project you are referencing. Only you know whether that is the case or not. You seem to be expecting a hard and fast ruleset about what is or isn't considered a project risk- you will not find that ruleset anywhere because projects cover a vast (probably infinite) range of activities and deliveries. What is a risk in one project will be out of scope in another project and, as answered in another of your questions, a project risk is one that could impact on your project goals (and objectives).
EDIT: When posting further questions it might be useful if you preface the question with a (very) short description of the actual project. This will help people to advise you on what is and isn't part of your project risk profile. Just saying.