You've had a statement from the club: They will be used for employees to gain admission to the stadium. - Whether you choose to believe that is another matter, but you've had the statement.
It may be using the system to recognise customers/fans (delete as applicable) goes against GDPR guidelines and the club statement will remain true, but it seems a lot of money to spent on new turnstiles when there are ongoing issues with people having non-NFC phones or phones where the NFC doesn't seem to work with the turnstiles.
Yep absolutely nothing dodgy about having 1 staff turnstile but all the rest have been fitted with facial recognition, all above board