'Expert' interviews of academics - Consent and Ethics
If you've had to go through ethics approval process, you are bound by the protocols that you come up with them. We've carried out interviews with other academics and are bound by ethics, and when I have been interviewed by other academics, I have gone through the ethics process. 

I would be skeptical if somebody was carrying out a research interview with me without obtaining formal approval from me.

As for your question:


  So, in asking for consent to record interviews and use the information for my research, do I need to ask each participant whether they want their contributions to be a) attributed or b) anonymized?


Your ethics board will probably approve the protocol you want to use. But yes, when I obtain permissions from interviewees, I usually ask three questions: (a) do they of their own free will agree to the interview; (b) do they agree to be interviewed; and (c) do they agree to have quotations in the paper that are attributed to them/anonymized to them/etc. (the last part depends on the study)

Sometimes a study has a mixture of anonymous and named participants.