Should someone with a history of hemolytic uremic syndrome as a child follow up with a nephrologist as a adult? even if they're not having problems

Yes : blood pressure need to be monitored together with kidney function test. So the answer is yes

Not necessarily: If your primary care doctor has checked your kidney function and it is normal then you probably do not need to see a nephrologist. If there is any residual kidney damage from the HUS then it would be good to see a nephrologist. Many people recover fully from HUS and do not need ongoing care by a kidney specialist.