In the telecom industry the rule is "silver on silver". Back in the bad old days there could be problems with diss-simmilar metals corroding & creating noise on circuits both from rectification effects & from current punch-through across the junction when voltage was applied to the circuit, i.e. "going off-hook". In some cases "sealing" current was (& still is) applied on a constant basis to circuits that didn't require it for operation, just to keep junction corrosion from getting bothersome.
Although not part of the original Bellcore standard I've actually speced tinned wire for T1 circuits going into areas I knew were going going to be climate controlled.
H.