Can one be an academic without having a job in a university? That's the question posed by Wanda Wyporska. A historian who left academia, she argues that the term should not be restricted to those with a university job; it is 'relevant to a broader constituency'. You can be an amateur historian with knowledge superior to that of a don; you could write books of history even though you don't have a PhD. So 'an academic outside academia' is a viable category.
I am assailed, here, by the spirit of pedantry. On the one hand, it is obvious that one can be an academic without a job in a university. For you can be an unemployed academic or a retired academic. On the other hand, these usages may be thought to be derivative, such that they allow academic status to people who either have had academic jobs or are in a condition that they might (again) soon get one; but the connection with academic employment remains vital.
Can't we just take our pick, therefore, as to whether or not we will use 'academic' in the way that Wyporska would prefer? Since there are already academics without academic jobs, we could choose to go with her preference and call amateur historians and such academics as well. Or we might wonder whether the status of 'academic' is that important in the circumstances. If you can be a historian, or a philosopher, or a scientist, etc, without being in university employment - which you can - isn't this good enough?