I'm going to be pedantic and challenge your use of the word 'learn' here. I tend to agree with the notion that being able to say 'I don't know, let me find out' and then find out quickly with a correct answer is in general a Good Thing™, but I wouldn't equate that with learning the thing they just looked up.

The difference between 'learn', 'cram', 'regurgitate' etc. depends on the level of understanding required, and the length of the recall.

And whether the interview is just asking definitions or silly certification questions, or things requiring deeper understanding.

Yeah, the disclosure is very important. It’s the difference between an open book test and notes written on their thigh.

During some interviews I’d give people access to a computer. If they could quickly find answers and solve problems, that is a skill in itself, but I could see what they were looking up. Sometimes that part would make or break the interview. Some people didn’t have a deep base of knowledge in the area we were hiring for, but they were really good at finding answers, following directions, and implementing them successfully. They would be easy to train on the specifics of the job. Other people couldn’t Google their way out of a paper bag, I was shocked at how bad some people were and looking up basic things. Others simply quit without even attempting to look things up.