I'm getting errors like the following in /var/log/messages from named:

Feb 11 11:20:31 foo.domain.com named[15446]: FORMERR resolving 'approvaltruthful.com/NS/IN': 59.63.157.212#53
Feb 11 11:20:48 foo.domain.com named[15446]: FORMERR resolving 'pt1.oceaninterdependent.com/AAAA/IN': 61.147.117.225#53

I believe these are malformed queries, but where are they coming from. This is on an internal nameserver where the address space is 192.168.1.0/24 and there is no access to port 53 tcp or udp from the outside. I'm assuming the IP addresses listed in the error message is where the request is coming from, but that doesn't make sense given that it's behind a firewall.

Any ideas?

These are indeed malformed dns queries (FORMat ERRor). They come from your dns server (foo.domain.com) trying to resolve a domain e.g. approvaltruthful.com For this, it queries the dns authoritative for that domain, or a forwarder if you have defined one in named.conf (that's the dns server 59.63.157.212). The reason the query is bad, could be a network problem, a misconfigured firewall in between or other similar problem.
The requests are coming from hosts using your dns. You can use tcpdump to find the host asking your dns for these domains and for what reason.

So, it sounds like there's not much I can do about it if the problem is on a device beyond my network, correct?

I run nslookup for the domain approvaltruthful.com and it came out without error. So if you're sure the problem is not on your side, then there nothing you can do.
You can use tcpdump to see from where the queries are coming just to be sure that there is nothing suspicious (like a spam bot) in one of your clients.
I also get tons of FORMERR and using tcpdump I've discovered that they are originating from spamassassin trying to resolve the domains that appear in email addresses or bodies in order to determine if the mail is spam or not. All I do is to filter out these errors from /var/log/messages.