UnsatisfiedLinkError exception loading native library: njni11
I googled it, but all I found were posts on how I needed to make sure I had installed the necessary packages, in particular libaio and libaio-devel. Well, I had all of those installed but I was still getting the error.
It finally hit me: I was automating everything (using Puppet), and hadn't explicitly configured those packages to be installed before Oracle. So they must've somehow gotten installed afterward. The Oracle install still succeeded for some reason, but dbca wouldn't run. Thankfully it was a VM, so I just told puppet to make sure the required packages were installed, reverted to my pre-Oracle-install snapshot, et voila!
Now time to figure out what these listener.ora and tnsnames.ora files are for and how they should properly be configured...