Notary Fraud-Company admits to in their press release today
A Notary Public is a public offical and as such they take an Oath of Office. When they don't do their job (check to see that the party signing a document is actually the party) they breach their oath and at the very least are liable for damages to anyone who relies on their seal.
If they knew that the person signing the document was not the real person then they are participating in a fraud together with the person signing the document. It is always a fraud on the part of the impersonator. It may be fraud on the part of the Notary Public, but in either case the Notary has liability and may lose their license.
(Now here's the big "IF") If it is actually the Notary's real signature. Many times with forged documents all the signatures are forgeries including the notary's. In that case the Notary will have to explain how their seal (unless the seal is a forgery) got on the document, which is why in addition to the notarial log referenced above a Notary should always keep their seal under lock and key