Global multi-tier supply chains face persistent social compliance risks, such as child labour and unsafe working conditions, because upstream supplier data is fragmented and difficult to verify. This paper proposes a socio-technical Digital Product Passport extension that encodes multi-tier social compliance attributes while explicitly supporting suppliers with low digital maturity through lightweight, evidence-based onboarding. The architecture integrates DPP data structures with ERP-triggered workflows and rule-based Robotic Process Automation to automate screening, documentation cheques, and escalation logic. For integrity and non-repudiation, a permissioned blockchain logs compliance decisions and anchors cryptographic commitments of off-chain evidence under access control. The framework is assessed through analytical and structural evaluation of decision determinism, rule consistency, and inter-layer coherence. Validation focuses on verifying that rule-based screening outcomes remain logically stable under incomplete, ambiguous, and heterogeneous supplier data conditions. The developed model illustrates that DPPs can be modelled as active compliance workflow components, not only traceability artefacts, by enabling structured evidence acquisition, rule-based classification, and auditable decision support across multi-tier supplier ecosystems.