If I had a nanny like this I would sack her immediately.
My son was in infant care since 4 mths old. If you're concerned about the focus given, the focus given by teachers are also not there because for most infant cares the teacher:baby ratio is 1:4. If there's a more needy baby (eg, just put in the infant care so cry alot) then the teacher will be busier with that baby than yours.
The other con is that my son fell sick very frequently. Almost every month for the first 6 mths that he was there.
The advantage of infant care is that it thought my child to be independent. My child learnt quite a lot of self help skills there, eg, taking toys and putting them back, holding his own bottle, following a routine.
In terms of educational involvement I think parents play a bigger role than the infant care. My son learnt most things at home through play and our constant repetition than he did in school I feel.
We didn't want to get a nanny solely because my husband and I are working and we cannot do "spot checks" on the nanny. I hate to be half-guessing all the time what the nanny is doing.