Aria Operations 8.18.x
VCenter 7.0.x and later
The permissions outlined in the documentation Privileges Required for Configuring a vCenter Adapter Instance is not enough for vCenter certificate information to be collected
curl -X GET 'https://<vCenterFQDN>/api/vcenter/certificate-management/vcenter/tls' -H 'vmware-api-session-id: <valid-vapi-session-id>' -H 'Content-Type: application/json' and check if it's responding back with certificate. If the response is 200 and the certificate is visible then the user has the required permission to fetch the certificates.