Many cases of salmonella in immunocompetent adults are minor, and we might just write it off as 'stomach flu' or 'grocery store sushi, that was a mistake' or something less.
I didn't mean to imply that the general risk was substantial (since I don't think it is, and I don't think the data says it is). I was correcting the 'snake v turtles' claim, mostly.
But as to the knowledge level of physicians, there seems to be a lot known about the risk of infection as related to specific immunosuppressive therapies -- for example " A higher incidence of salmonellosis is seen also in patients with antibody deficiencies, defects in cell-mediated immunity and deficiencies in Th1 cytokines (IL-12, IFNγ) or cytokine receptors (IL-12R β1 subunit, IFNγR chains 1 and 2). " A physician prescribing immunosuppressive drugs might have reason to try to avoid one of the cytokine inhibitors if there's even a slightly elevated baseline exposure to Salmonella (or not; they could do the math on that).
It might depend in part on the condition being treated, such as the combined effects of disease and treatment in lupus. I'm sure there are many more specific considerations, and physicians tend to know a lot of this sort of stuff right off the top of their head (a visit to my rheumatologist is always a lesson in how much detail he knows).