Checking back on my own question. It's probably evident I'm stumbling around blind, but I added BACKLIGHT_ENABLED = yes to my Makefile which promptly broke the build. Stops with error 'BACKLIGHT_LEVELS' undeclared. Setting that in config.h allowed the build, but none of the firmware shortcuts (BL_TOGG, BL_INC, etc.) seem to work, so it seems infinity60 is not setup for LEDs out of the box in QMK.
I'm not a C programmer, so I'm probably out of my depth here, but I'm going to dig into the Whitefox LED code from a prior build I did to see if that yields any hints. Any suggestions are welcome!