Can I attempt to match members by uploading a CSV file that contains Salesforce ID into Swift Digital?

Unfortunately, no.

Members that are sync'd between Salesforce and Swift Digital use Swift Person ID and not Salesforce ID.

Swift person ID is a system ID and will not correspond with any uploaded information from any format (CSV eg.).

Swift person ID and Salesforce ID uploaded from a CSV file are kept in custom fields, and as such they will not be used to compare with System IDs.