Mmmm, nothing in RAW suggests this to be true. By RAW each and every effect (which may impose multiple conditions, penalties, damages, etc) is entirely independent of every other one. So if you take ongoing 5 poison damage (save ends) twice, you will only take 5 points of damage (because ongoing damage of a type doesn't stack) but you would have to save against each one independently.
FWIW, I agree with this interpretation.Mmmm, nothing in RAW suggests this to be true. By RAW each and every effect (which may impose multiple conditions, penalties, damages, etc) is entirely independent of every other one. So if you take ongoing 5 poison damage (save ends) twice, you will only take 5 points of damage (because ongoing damage of a type doesn't stack) but you would have to save against each one independently.