The GDPR legislation requires the need for consent to process personal data. Therefore in order for ProSites to be compliant, it will need an unticked checkbox asking for permisson to process the data on the registration / signup page (wp-signup.php).
1) If the user does not consent by ticking the checkbox they should not be allowed to register.
2) If they tick and consent, then the date and privacy text they agreed to should be stored in the database to track their consent.
Can you confirm whether or not the developers will have this implemented by May 25th?
PS it would be better to have the ability to add multiple checkboxes to allow the network admin to request consent for other uses of the data such as marketing or signing them up to a newsletter with their email address...