Please contribute more to this if you have additional information.
After discussing with some other users it seems that /dev/gpio has disappeared in backfire, at least on the ar7xxx devices (ubiquiti, linksys wrt160nl) that we've been testing. In order to manipulate the LEDS without gpioctrl, one needs to write directly to the led's file in /sys/class/leds. Here's an example of turning the red led on using the ubiquiti picostation m2-hp with directory contents listed:
root@fabfi1:/# cd /sys/class/leds
root@fabfi1:/sys/class/leds# ls
ath9k-phy0::assoc ath9k-phy0::rx ubnt:green:link3 ubnt:orange:link2
ath9k-phy0::radio ath9k-phy0::tx ubnt:green:link4 ubnt:red:link1
root@fabfi1:/sys/class/leds# cd ubnt\:red\:link1/
root@fabfi1:/sys/devices/platform/leds-gpio/leds/ubnt:red:link1# ls
brightness max_brightness trigger
device subsystem uevent
root@fabfi1:/sys/devices/platform/leds-gpio/leds/ubnt:red:link1# echo 1 > brightness
root@fabfi1:/sys/devices/platform/leds-gpio/leds/ubnt:red:link1#