What is a DNS seed node vs a Seed Node? I've seen references to both strewn around. Specifically, is there a bitcoin client running at the DNS seeds or seed nodes?
As you correctly identified, there are two types of seed nodes, i.e. DNS seeds and seed nodes. DNS seeds are stored in chainparams.cpp. As of today (April 2017) the following nodes are listed in this file.

seed.bitcoin.sipa.be
dnsseed.bluematt.me
dnsseed.bitcoin.dashjr.org
seed.bitcoinstats.com
seed.bitcoin.jonasschnelli.ch
seed.btc.petertodd.org

I performed nslookups on these DNS names and they return a list of IP (14-26) addresses that all seemed to be running bitcoin nodes.
There is also the concept of seed nodes which are hardcoded IP addresses in the event that someone is experiencing a DNS failure or other issue.  These nodes are only contacted if no other discovery mechanism works.