Hi Tam
Depending on which Moodle Version you are using here are some thoughts.
We are just looking into implementing such a thing and at this stage it's a combination of Activity Completion for the Survey and Restrict Access for the Assignment submission activity (won't work for any manual grade items).
For the Survey - see Activity Completion (https://docs.moodle.org/30/en/Activity_completion_settings) screen shot
For the Assignment submission activity see Restrict access screenshot. This would need to be set for all Assignment activities and of course enabled after submissions have been received. A bit labor intensive to manage.
Two other manual approaches
Another approach is to use the Marking Workflow (https://docs.moodle.org/30/en/Assignment_settings#Use_marking_.28grading.29_workflow) and only 'Release' grades manually when the survey is completed. Per user option
Or simply hide the gradebook results with the eye closed (In Grader report with editing turned on) manually until Survey completed but this is set for all enrolled users in the course.
Any other ideas?
