With IP addresses, there has to be a need for them, there has to be justification, because the end result, is that the justification has to go back to ARIN, who provides IP addresses to datacenters and hosts throughout the world.
Perhaps the client is doing some sort of dedicated hosting or will be running VPS machines from a dedicated server. With our dedicated servers, we can use anywhere from 10-50 IPs one 1 individual server, for VPS machines and some VPS machines need multiple IPs for various reasons. So, you can actually utilize alot of IPs for just 1 dedicated server.
Just make sure that your client provides justification and you supply that to your hosting provider as well. This is a requirement, not just for you and not just for your host, but it comes from ARIN, who provides the IPs to everyone, they must have that for every single IP that is assigned to everyone.
Good luck with your business!