Varying nameservers within a private blog network?



It is best to take precautions and minimize footprints, but nothing that you do can grant you immunity or guarantee 100% against being found and penalized. Instead of using a single SEO host, it is a better option to use normal shared hosting accounts but things could get expensive.
 
I am a fan of Amazon's Route 53. They give you a random set of nameserver domains (4 tlds, approx 1000 domains on each, approx 1000 subdomain combo's on each of those). That keeps things pretty random. And if Google has Route 53 detection built into the algorithm, it's not a big deal as a good chunk of the internet uses it already

Amazon Route 53 Usage Statistics
 
For a private blog network I'd prefer to use a bunch of different nameservers instead of just the host/registrar's nameserver.
 
Stick them on the free version Cloudflare and use their DNS servers. One of the biggest DNS server networks in the world, nicely disguised and it will speed up your sites :)