Hybrid power plants combine dynamic response assets such as wind power, photovoltaic systems, battery energy storage systems and STATCOMs under the supervision of a Hybrid Power Plant Controller. The ability of such plants to provide grid code compliant ancillary services depends not only on the control design of the Hybrid PPC, but also on the interoperability characteristics of the individual assets, including communication latency, controller processing delays and inverter response bandwidth. This paper investigates interoperability aspects in HPPs providing voltage control and power oscillation damping services. Different HPP control topologies and cascaded control architectures are analysed, with particular focus on the impact of communication and control delays between the Hybrid PPC, subsidiary controllers, and dynamic assets. Transfer function based analyses and model based assessment studies are used to evaluate the influence of interoperability limitations on voltage control performance and POD-Q behaviour under representative grid code requirements. The results show that voltage control can tolerate moderate delays while still complying with response time, settling time and overshoot requirements, whereas POD-Q performance is significantly more sensitive because additional delays directly introduce phase lag into the damping response. Based on the analysis, recommendations are provided regarding communication architectures, controller integration and asset qualification to support reliable implementation of voltage control and POD-Q functionality in multi-vendor HPPs. The paper intends to contribute to improved grid code compliance and more robust operation of future HPPs.