They brag about "99.9999% uptime history" at http://www.dnsmadeeasy.com/technology/.
Though they doesn't seem as innovative and nice as DNSimple. Really hope things work out for DNSimple (really like the idea of their beta feature GitHub sync).
(I wrap Amazon's route53 with DNS entries read from github/gitbucket/similar.)
An interesting/custom choice to use JSON, and real github integration rather than using hooks as I did.
However, making your DNS servers to be responsible for serving their own DNS is a bit of an extra complexity and risk that no customer will ever care about..
http://aws.amazon.com/blogs/aws/route-53-update-private-dns-...
"You can create generic "white label" name servers such as ns1.example.com and ns2.example.com, use them in your delegation set, and point them to your actual Route 53 name servers."
Does that answer the question? I'm a little hazy on what you're actually asking.
Their interface is pretty bad, but the backend is hardy.
If I do a traceroute to the 5 DNSMadeEasy name server records (they actually run many more hosts) I go via 3 different networks - GTT, NTT, and Tata.