This paper evaluates voltage regulation coordinated across advanced distribution management systems (ADMS), distributed energy resources (DERs), and distributed energy resource management systems (DERMS) using an advanced hardware-in-the-loop (HIL) platform. The HIL platform provides a realistic laboratory testing environment, enabling accurate dynamic modeling of a real-world distribution system from a utility partner, with real controller (ADMS and DERMS) and power hardware (DER) and standard communications protocols. The test results show proper performance of the voltage regulation by coordinated control systems and confirm correct functioning of the HIL platform. With this laboratory capability, utilities can test grid automation systems that can manage DERs to achieve system-level control and operation objectives (e.g., voltage regulation). This HIL testing capability will help mitigate risks of potential issues (e.g., instability) during field deployment.