Just like any veggies I eat, I always wash them thoroughly first. But for salmonella, it mostly depends on what you are feeding them, and how you handle the plants. If you are using animal waste in your
nutrients (fish emulsion, bat guano, chicken poop, etc.) there's a risk of salmonella. Also any organic nutrients, because organic nutrients are made from animal waist products. If using these products, it can also be spread if you touch the plants with the water, or accidentally splash it onto the leaves.
How you handle your plants in a aquaponics system is important for that very reason, they use fish waist as the fertilizer (nutrients). Here is a pdf. about that :
On-Farm Food Safety: Aquaponics, by the university of Hawaii.
P.S. salmonella can also be spread by any animals that may defecate on your plants. Birds flying by pooping on them, rabbits, mice, squirrels etc.. That will be possible weather you grow in soil or hydroponics. But growing inside you have more control about animals around your plants. But like I said, I wash my produce thoroughly before eating it (homegrown, or store bought).