I think the legal ramifications of refusing to provide emergency treatment when there is an already established VCPR vary depending on location. My own state, Tennessee, does not seem to require it, but a small sampling of a few who do follows:
Louisiana's Veterinary Practice Act states:
With regards to emergency care, please refer to the Practice Act's Section 1518A(9) granting the Board the power to adopt rules of conduct, and Section 1526A(14) regarding unprofessional conduct. Board Rule 1001A does, in fact, adopt the AVMA's Code of Ethics. Principle II.F of the Code of Ethics states, in pertinent part, that "in emergencies, veterinarians have an ethical responsibility to provide essential services for animals when it is necessary to save life or relieve suffering."
The Board interprets this responsibility, in general, to mean that the veterinarian must stabilize a true emergency condition regardless of whether it is an established patient or not. Such must be done without concern for compensation. In the event services are then needed beyond the stabilization, the veterinarian may demand payment (or arrangement for payment) for further services prior to provision of such services.
From the New Jersey State Board of Medical Examiners:
All licensed veterinarians must provide emergency
care.
Georgia:
700-12-.06 Emergency Coverage.
(1) A licensed veterinarian employed at a veterinary facility must ensure that emergency treatment or access to emergency treatment to clients with an established veterinary-client-patient relationship is provided.
So while it's true that the AVMA's Principles and Practices are ethical guidelines and not laws, some states have, in fact, adopted these guidelines in their State Practice Acts, which does then carry legal ramifications for failing to act ethically.
As to the OP, I think the question is designed to determine whether or not you are familiar with the AVMA's guidelines.