At first, I would say, theoretically, certificates are not that important for designing a secure infrastructure, as a certificate is just a kind of official document confirming some facts such as competence of an individual or an organization. In other words, it is optional.
Of course, however, digital certificates are essential for building a secure infrastructure. We know that is another story. :-))
In regard to the role of standards in designing a secure infrastructure, I would say it is not only important, it is essential, as standards are the best practices that have been widely recognized and well proven by authorities and experts all over the world. Standards tell people how to do the right thing in the right way.
Basically, standards are essence of knowledge.
Therefore, the best practice to do something is to follow the standard. The same for designing a secure infrastructure.