The main thing is your use is outside StartCom's policy. See https://www.startssl.com/policy.pdf

> Class 1 certificates are limited to client and server certificates, whereas the later is restricted in its usage for non-commercial purpose only. Subscribers MUST upgrade to Class 2 or higher level for any domain and site of commercial nature, when using high-profile brands and names or if involved in obtaining or relaying sensitive information such as health records, financial details, personal information etc.

StartSSL will make you pay to revoke a certificate if you need to.

They have some sort of regex they use to flag business domains. For example, if your domain contains the word 'billing', then they won't give you a cert.

they reject the certificate request if they check the domain and there's content indicating it's a commercial business.

if it's an empty site then you're ok.