One Nameserver for all my servers

Having a single nameserver generally is not something you would want to do, and not something that ISPs recommend. It means that when your website is being queried, only a single server would serve up the underlying dns information: If that server went down, your systems would not be availalbe to end users trying to get to your website.

It seems like what you want to do is have your clients put in a CNAME record for their website to point to the DNS name of your load balancer. the load balancer would then be responsible for distributing traffic to the underlying EC2 or non-EC2 environments.