I suspect that D cannot do that legally.
Section 13 of the license (Offering the Program as a Service) provides that:
If you make the functionality of the Program or a modified version available to third parties as a service, you must make the Service Source Code available via network download to everyone at no charge, under the terms of this License. Making the functionality of the Program or modified version available to third parties as a service includes, without limitation, enabling third parties to interact with the functionality of the Program or modified version remotely through a computer network, offering a service the value of which entirely or primarily derives from the value of the Program or modified version, or offering a service that accomplishes for users the primary purpose of the Program or modified version.
“Service Source Code” means the Corresponding Source for the Program or the modified version, and the Corresponding Source for all programs that you use to make the Program or modified version available as a service, including, without limitation, management software, user interfaces, application program interfaces, automation software, monitoring software, backup software, storage software and hosting software, all such that a user could run an instance of the service using the Service Source Code you make available.
It seems to me that the hypothetical business plan violates section 13 of the license if the "Service Source Code" is not made available to each and every user. Whether D and D's associates plan to make, or in fact do make, a profit is irrelevant. The license requires releasing such source code even if the service is made available for free. If D is not willing to make such source code available, then D would be wise to use a database program available on different terms.
Note that if D merely intends to run the DB program on D's own servers, but not provide access to the functionality of the DB to users, then there would be no requirement to provide any source code to anyone under the linked license. Whether the app in fact "provides access to the functionality of the DB" will depend on the exact function of the app, and may be a question of interpretation of the license. From the very brief description of the app in the question, it seems to me that it would. Before undertaking any such plan, D or anyone in D's position would be wise to consult a lawyer knowledgeable in open-source license law as it is applied in D's jurisdiction (which is not stated in the question at this time).