Agreed - We have a ergo, and yes, they position babies/toddlers in the same position as a manduca. I did my research pre purchase as DS was a Hip dysplasia bub so there was no way I was taking any risks with DD. These types of carriers that position bubs in a frog type sitting position actually discourage hip problems rather than cause them so your friend is quite misinformed here.
I would not however use a baby born etc that lets the legs dangle as mentioned as these would not be good for hip development at all.