Dr Singh, interesting question. Salmonella perhaps secretes lytic enzymes packed into bacterial outer membrane vesicles. It would be nice to find out if unwashed erythrocyte samples contain some signals that inhibit secretion of these lytic enzymes.
Libby and others, reported a salmolysin of 16 kDa molecular weight to be hemolytic and cytolytic a in S. Typhimurium.Another haemolysin reported in Salmonella strains is cytolytic phospholipase و It induced lysis of RBCs, (pore forming cytotoxic protein) alouthgh you said that Salmonella strains lyse washed RBCs but rarely unwashed ones,but serovars like Typhi and Paratyphi A have been reported to haemolyse unwashed erythrocytes too , but note that not all serovars have capability to lysed RBCs (washed or unwashed). I'll give you example, Failure of 45 strains to lyse chicken RBCs which may be due to lack of receptors on chicken RBCs for haemolysins of S. Gallinarum .