Schoolrunner's Gradebook is designed to only show assessments that factor into student grades. It will not show any assessments that are outside of a course's grading methodology.
However, using the Google Classroom integration, it is possible to sync in assessments that do not count for grades. Note that these assessments still will not show up in your Gradebook, but they will be accessible elsewhere in Schoolrunner, such as on the Analysis page or the Assessments page.
When syncing in an assessment from Classroom, you'll see in the "Assessment Type" menu a "Counts for Grades" section and an "Other" section. These sections are only available when syncing from Classroom; adding an assessment manually in Gradebook will not provide you with these two sections – you'll only see assessment types that count for grades.
Assessments tagged to an assessment type from the "Other" section will not appear in your Gradebook once you've synced them in. But they will be in Schoolrunner! You can find them on the Assessments page or on the Analysis page. You can still sync in updates for non-grade assessments, either individually by clicking the "Update" button next to the assessment name in the Classroom window, or by clicking the "Update All" button (which updates all assessments previously synced in from Classroom, whether or not they count for grades).