Can I effectively mask/redirect to Linode's nameservers using my domain? I have clients set to ns1 and ns2.mydomain and if I move them here I'd like to keep their nameservers the same if possible. It isn't a huge deal, but if I can do it that's the route I'd rather take. Am I nuts?
First off, I assume we're talking about DNS servers that service the domains in question (e.g., client domains) and not that you give those nameservers to clients to use as resolvers.
Presumably, today, each client's domain registration (whois) has ns1 and ns2 as the two nameservers, with glue records pointing at the IP addresses of whomever's nameservers you currently use.
I don't think there's anything stopping you from changing those glue records to point to Linode's nameservers (or at least 2 of them), and if you first populated Linode's nameservers with your client's domain records, everything should keep working once the registrar update propagates.
With that said, you're then responsible for maintaining those glue records in sync with the actual IP addresses used by the Linode nameservers, which seems risky to me (though I'm not sure to date they've ever changed). Presumably that's already the case with your current provider, though they may also specifically provide servers with addresses assumed to be referenced through such means.
This assumes ns1/ns2 are currently run by your current provider. If in fact, you're hosting them on your own machines (thus the glue records point to machines you control), that's more robust, since you can re-point them at Linode's you control and since you handle both the actual host (and its IP address) and the glue records, there's less risk of mismatch.
But sans owning the servers yourself, better would be to just changing the registrar data to use the Linode nameservers by name, and avoid the glue records, though you'd have to give up the vanity nameservers in that case.
You "register" name servers with their ip address, I do it on all of my linode sites. You can even glue IPv6 on the linode name servers that are IPv6. (As of this writing, that's ns1, ns2, ns4)
There is a caveat, some top level domains do not support alias's for registering name servers.. I only did IP routing stuff for about 6 months. I believe there are issues with this setup, and .org domain names.