That will work, however, it would be smart to include some static text into that keyphrase as well to make it unique to that specific scheduled action. Such as "Inactivity follow up email for member [member:id]".
Otherwise, if you try to schedule other unrelated actions for a member just using the [member:id] as a keyphrase, then it will potentially overwrite an existing scheduled action with that member id that it has no business overwriting.