No, evidence from a CI is not admissible when the CI is not revealed to the court. I'm not saying parallel construction applies to every case involving a CI; I'm saying it applies to cases made from CIs who remain sources after the case is brought, and are thus concealed from the court and (more importantly) the defendant.
Again, the distinction is that the use of the CI is not a violation of the defendant's constitutional rights. Hiding the existence of the CI doesn't have the effect of hiding a constitutional violation by law enforcement.
