What makes you think that the Open University is run by Harvard? I have never heard that suggested before. As far as I am aware, the Open University runs itself and is not run by any other university.
OP, there is a possibility that some law firms or chambers might be sniffy about an Open University degree, but many are now assessing applications university-blind. I know someone who obtained a first in Law at the Open University, then did a BCL at Oxford, and is now practising at the Bar.