Yes, to both questions. In theory, a .38 Special bullet is.357" and a 9mm Luger is .355, but people who insist on such precise figures have never heard of tolerances. I have loaded many rounds of .38 Special (and .357 Magnum) with 9mm Luger bullets and the only problem is that most 9mm factory bullets have no crimping groove so they need a tightly sized case to prevent bullet jump. Cast 9mm bullets have a groove, or at least mine do.
FWIW, Ruger made/makes a Blackhawk convertible in .357 and 9mm. Mine shoots fine with either.
Jim