The rapid advancements in cloud computing and other next-generation information and communication technologies have fueled the swift development of data centers (DCs). Aggregating these DCs to form virtual power plants (VPPs) for supporting grid frequency regulation has substantial potentials. However, previous research on DC frequency regulation has overlooked two major issues: inadequate consideration of clustering analysis for geographically dispersed DCs with similar load characteristics, and neglecting the influence of uncertainty within communication networks on power dispatch strategies for frequency regulation. To address these issues, this paper proposes a novel co-design method for power dispatch and communication transmission to facilitate frequency regulation for multiple VPPs based on DC aggregation. First, a DC aggregation strategy based on Ng-Jordan-Weiss spectral clustering algorithm is devised to construct the VPPs aggregated by DCs and determine their aggregation regulation capability. Based on this, a joint design approach is developed, which integrates a power dispatch strategy considering communication network uncertainty with a routing path optimization scheme for mitigating the network uncertainty. The method obtains precise power regulation tasks, thereby ensuring the reliability of VPPs' frequency regulation. Finally, comprehensive simulation results substantiate the viability and efficacy of the proposed methodology.