IANAL, k? And, the devil's in the details, as they say, but...
The whole thing seems to hinge on the concept of reasonable expectations. As suggested by the phrase "two-party consent", the law against secret recording came from folks who, having participated in a one-to-one conversation on the phone, or other private setting, and believing that in that scenario they had a reasonable expectation of privacy, had their expectations upended by the other party, or some third party, making audio recordings of the conversation. In other words, it protects private individuals who believe they are conducting private conversations from having their expectations abused.
However, a police officer, as a public servant who, among other functions, is tasked with creating public documents, tickets, citations, incident reports, arrest reports, etc., would have no basis for forming a reasonable expectation of privacy in the execution of the officer's public duties.
Audio vs visual recording, concealment of microphones, etc. are just red herring issues for derailing the logic train before it pulls into Common Sense Station.