I’ll need to have all SFDC Channel Partner Account Records and corresponding Channel Contacts assigned to Matthew McLarty. My question is how can I identify the channel partner accounts from the regular accounts.
Partner created Account or Contact records can be identified using merge field
CreatedBy.UserType field on User object.
UserType value is based on the User's license and partner users will have value as 'PowerPartner'. Please check Salesforce docs for various values of UserType field.
You can use Process Builder to evaluate the Account and Contact records for CreatedBy's UserType value and re-assign the record's owner.