Hostgator helped me set up two nameservers for my first server, but I don't get any replies from them when i ask about setting up two more nameservers for a second server, how can i do this?

Are they dedicated servers? You could just create ns1.yourdomain.com and ns2.yourdomain.com and point them to the 2 IP addresses for the server.

Or use the existing nameservers also for the second server.

so if i create a redirect of ns4.mydomain.com and point it to my.ip.000.000.000 it would work like a nameserver....?

when i tested it, i got an error "The name server is not sufficient or hasn't been approved."

What is your server's OS and control panel your using?

so if i create a redirect of ns4.mydomain.com and point it to my.ip.000.000.000 it would work like a nameserver....?
How point to IP? You did not provide enough informations to get exactly what you did but this above looks like ordinary A record, not registering new nameservers with your domain register.