Legume crops are agronomically vital, yet soil salinization severely suppresses growth and nodule formation. In this study, a rhizobium isolated from lablab nodules, Ensifer sp. (R1), and a wetland-derived halotolerant bacterium, Oceanobacillus aidingensis (OC2), were co-inoculated onto lablab to investigate their synergistic effects on salt tolerance and nodulation. Both lablab and R1 were sensitive to salinity, but co-inoculation (R1+OC2) produced significantly greater biomass under salt stress than either single inoculation. Co-inoculation also markedly increased nodule number and enhanced peroxidase (POD) activity and flavonoid accumulation in plant tissues. Further analyses indicated that metabolites from OC2 protected R1, substantially improving its salt tolerance, and stimulated R1 to produce more indole-3-acetic acid (IAA), thereby supporting plant stress mitigation. OC2 additionally promoted root-hair density and flavonoid accumulation in lablab roots (up to a 55% increase), strengthening rhizobial attraction signals and improving nodulation efficiency. Lablab roots exhibited clear tropism toward microbe-inoculated soil, and OC2 may enter nodules to utilize carbon and nitrogen sources provided therein, forming a distinctive microbe–microbe–legume mutualism. Overall, this work demonstrates that interspecific microbial synergy can effectively enhance crop resilience to stress, offering a new strategy for the sustainable management of salinized farmland.