No. As long as the API name for the field in Salesforce is the same on both the Lead and Contact objects, you do not need multiple mappings. HubSpot uses the API name to identify the correct field when syncing values with Salesforce.
During the initial sync between HubSpot and Salesforce, HubSpot searches Salesforce for records with a matching email address. After the initial sync, HubSpot will continue to sync with the most recently updated record in Salesforce with a matching email address, even if that record is converted from a Lead to a Contact in Salesforce. Please note that it is not advisable to create duplicate records in Salesforce. For more information about how the HubSpot-Salesforce integration handles duplicates, check out this article.