I asked other RNs on the unit about fundal checks on c-sections, as well. Most of them have been there for many years and they all said it's policy not to do them, but no one can say why.
I will take a look at the P&P, as suggested (I feel silly for not having looked it up sooner!). I'm going to do some research on this as well- I don't want to rock the boat as the 'new girl', but if this is really the policy, it should be changed asap.
And I'm going to continue doing my fundal checks on everybody.