Should I be concerned if my 6 week old just got the rotavirus vaccine and my 19 month old sucked my 6 week olds dummy.?

If symptoms see MD. It should be alright, but if you notice any symptoms such as vomiting or diarrhea, please follow up with your M.D.
I wouldn't. The 19 month old is unlikely to have problems from this action. True, the rotovirus vaccine particles may pass in babies diapers for 6 weeks after each dose, but its chance to produce disease is negligible. I anything, the 19 mo may get a free rotovirus vaccine dose.