This work investigates the optimality of compress-and-forward (CF) type relaying in wireless networks when the relay does not know the codebooks used by the sources. The relay is called oblivious for this reason. The relay-destination links are assumed to be out-of-band with finite capacity. We study two multi-source relay networks, namely the multiple access relay channel (MARC) and the interference relay channel (IFRC), both with an oblivious relay. For the MARC with an oblivious relay, we derive a new outerbound and show that the capacity region can be established using a generalized CF (GCF) scheme, where the destinations jointly decode the compression indices and the source messages. In particular, we observe that, for multi-source relay networks, GCF scheme achieves higher individual rates than the conventional CF scheme with sequential decoding of compression indices and source messages. For the IFRC with an oblivious relay, we focus on the case where the destinations know all the codebooks used by the sources. We establish a new strong interference condition, under which we derive a new outerbound and show that it is achievable using GCF scheme, thus establishing the capacity region of IFRC with an oblivious relay.