I was finally able to resolve this. So that maybe other users can find how to fix this if they run into the same issues:
tl;dr:
Edit the virtual machine in question, go under Console, make sure SPICE is chosen for graphics, and under "USB Redirection" choose "Native." When you reboot the VM, it will have both UHCI and EHCI (2.0) controllers. Now, any USB 2.0 devices that you attach will work correctly.
Long version:
I struggled with this for quite a while. While doing some additional research, I found a note in the 4.1.0 release notes referencing BZ 1373223. This particular note was for ppc64 architecture systems, but it curiously said that enabling USB Redirection under SPICE would change the USB controllers available on the host. I dug a little deeper into the bug thread and found a couple of references that seemed to indicate that x86/x86_64 exhibited the same behavior. Apparently, UHCI (1.1) is the default because it supports SmartCards, but the EHCI (2.0) controller does not. So, turning on USB Redirection under SPICE settings for the console enables an EHCI controller, thereby enabling devices that require USB 2.0.
Personal opinion:
This is really obfuscated. It would be great if this switch lived somewhere more obvious. Even if that doesn't happen, this should exist in a document somewhere. Maybe it does and I couldn't find it, but I tried!