Decentralized Multi Agent Reinforcement Learning (MARL) faces a fundamental dilemma in real world deployments: agents must operate under epistemic fragmentation, where local observations are severely occluded, while navigating heterogeneous value landscapes, where sparse, critical events carry disproportionately high stakes. Existing paradigms typically decouple state estimation from policy optimization, guiding perception modules merely to minimize uniform reconstruction error. This leads to a Perception Value Misalignment, where agents squander computational resources reconstructing task irrelevant background noise while failing to resolve uncertainties in high value regions. To bridge this gap, we propose EVA-Gen (Epistemic Value Alignment via Generative Models) that establishes a cybernetic loop between generative perception and value based decision making. We formulate the Value Conditioned Reconstruction Paradigm, establishing that optimal perception under resource constraints is functionally weighted by the gradient of the value function. EVA-Gen couples Backward Flow to steer diffusion toward high stakes manifolds, Collaborative Information Bottleneck to filter communication for value relevant consensus, and Risk Sensitive Rectification to prevent sparse signal dilution, synergistically closing the perception control loop. Empirically, we demonstrate that EVA-Gen achieves superior performance in three value-heterogeneous multi agent environments.