You can surely setup your name-servers in one server and use the same for the other using the cpanel inbuilt DNS Cluster feature( WHM >> Cluster/Remote Access >> Configure Cluster). But, It is better if you,
Configure nameservers as,
ns1/ns2.yourdomain.com --> server 1
ns3/ns4.yourdomain.com --> server 2
Cluster the DNS using the DNS Cluster option in your WHM.
Use these four nameservers for your domains at your registrar.
By this way, if one of your nameserver server fails, the other will successfully serve for DNS requests(ofcourse there is no use, if the whole server is going to fail, unless you have proper mechanisms configured to handle such instances in place).
DNS Clustering Doc: http://docs.cpanel.net/twiki/bin/view/AllDocumentation/WHMDocs/ConfigureCluster