yes, you can access GPIO via ruby.
I don't know, if my way is the correct one, but I got it running.
First install wiringpi from https://github.com/LeMaker/WiringBPi
When you compile and install this, you can test your GPIO pins with "gpio".
Then install the ruby gem:
gem install wiringpi
If you have luck, then you can access GPIO with ruby.
On my side, I had to copy
to the gem directory under /var/lib/gems/1.9.1/gems/wiringpi-1.1.0/ext/wiringpi/
Just overwrite the existing ones here.
Call "make" and "make install" in the same directory and then ruby should work
You can have a look on my little blog at http://www.pinkware.de/?p=43.