How to run dns seeder?
I realize this question is a couple years old, but a proper tutorial has never been written until now. The tutorial is somewhat large, so I won't re-post it here, but I wrote a step-by-step guide for setting up a DNS seeder that you can find permanently hosted here: https://github.com/team-exor/generic-seeder/blob/master/SETUP.md.

The instructions are written for a clone of the original bitcoin-seeder called the generic-seeder, which is a modified clone of the bitcoin-seeder that makes it easier to set up a DNS seed for virtually any alt coin by using a config file.

As far as why your seeder isn't working, part of it seems to be because you may not have created the proper DNS records. You say that you created:

dnsseed.example.com -&gt; IP


but it should look more like this:

dnsseed.example.com -&gt; vps.example.com -&gt; IP


vps.example.com: "A" record that points to your server IP address
dnsseed.example.com: NS record that points to your "A" record (vps.example.com)

Once your two DNS entries are created, you can run the seeder app like this:

./dnsseed -h dnsseed.example.com -n vps.example.com -m test@example.com


test@example.com: this can be any email address and is only used to serve SOA record data from the local DNS server that the DNS seeder app is creating. 

Full disclosure if it wasn't already obvious: I am the author of the generic-seeder.