Because patients have the ability to enter (as free-text) the name of any insurance company they are with (including international insurers) there isn't any common list that the online registration form can share with the names of the insurers you already have in the SPM application. There is no direct link between the online registration form and your database. The import application does try to match the name of the insurer with an existing contact in your database, but it appears that NIB is the most common match.
When importing a patient's registration form, on the Import screen the 'Health Fund' field in the left-hand panel will have the text that the patient has entered; on the right-hand panel the 'Health Fund' field has a list of all the third-party contacts in your database that you have marked as being a health-fund/insurer. If there is an exact match (or even a best-match), the correct insurer will appear in the Health Fund field of the right-hand panel.
Health Fund/Insurer selection list from SPM:
If there isn't a match you will need to use the drop-down option to select the correct insurer from the list. If the insurer is not already in your database you can add them in Setup > Contacts > Health Funds.
If you have already imported the registration form and want to check what the patient had actually entered, you can retrieve all of the data they put onto the form by going to the patient's Notes, selecting the 'patient Registration' record and click on the link below the heading 'All form data'.
This pdf includes all of the information the patient provided to you as well as the text of the Authorisation section of the form.