Hi mattc,
I can not help you with oxfGPIO, but I did several projects with wiringPi, which is easy to use and has a great website (http://wiringpi.com/) with explanations. I don't know if you can switch, but I'll describe nevertheless:
Just install wiringPi like described on the webpage (I did this on Pi B+ and Pi2 on different raspbians without ever any problems).
Then in the config.make of your OF app uncomment the line:
PROJECT_LDFLAGS=-Wl,-rpath=./libs (around line 80)
and add the line
PROJECT_LDFLAGS += -lwiringPi
Then in your ofApp.h add
#include "wiringPi.h"
That's alrerady it.