Thanks for the link gabriele. I looked over it, but it didn't quite clear up everything. The chart they provide does a little compare-and-contrast between NIS and LDAP, but never explicitly mentions whether LDAP can be used for user authentication. The reason I was still hesitant is because they also included DNS in the chart, and I'm fairly positive (though not 100% positive) that DNS can't be used for authentication.
After some more poking and prodding on my own, I hit pay-dirt.
LDAP Authentication for Linux
That page gives instructions to set up an LDAP server to provide user authentication. Since it requires installing libnss-ldap and pam-ldap, I get the idea that user authentication was a concept LDAP wasn't necessarily created for, but sort of shoe-horned into it. Anybody stumbling onto this thread that wants to know where to get the stuff mentioned in the article linked:
Padl open source software - pam-ldap, nss-ldap, and other pieces of software
Here's another site that looks to explain how to configure a system for LDAP authentication.
Authenticating with LDAP
Note: I have not actually put either of these instructions into practice (yet). So I cannot vouch for them.