Yes, the summary email can be disabled with the disable digest emails site setting.
The use of the term ‘digest’ for the summary email site settings could be somewhat confusing. The reason that ‘digest’ is used instead of ‘summary’ on the settings page is because the summary email used to be called the digest email. Maybe this is something that should be changed on the settings page.
Have a look at this topic for details: Discourse Activity Summary Emails Guide.