A Rabbit pen may not just contain Rabbits! But it's function is to provide a place where wildlife can always be found for training steadiness and working anongst distractions. Imagine retrieving a dummy with rabbits running around!
Most people dont have access to that kind of thing, but we still do what we can. Walking in an area of high rabbit density, doing stays in a wood where there are lots of Squirrles, walking through a chicken run or beside a Pheasant pen. All ways I use to the same end.
Yes it does count Mo. It's just one step along the way. Often the top trials people get some of the investment back by hireing a Rabbit pen out to groups and clubs. But with a little lateral thinking you can probably think of alternatives. But the big thing is to not tolerate "Chasing" whilst at the same time encouraging controlled "Hunting."
All the steadiness training that you do throwing dummies around over heads, tennis balls etc. does the same sort of job. If you can get your hands on some cold game you can do the same thing.
I have never had any of my dogs in an actual "rabbit pen" but they are still steady.
A good one to start with for Bracken is if you can get your hands on a rabbit, tie a bit of string to it and pull it across in front of her making sure she remains steady. You just have to improvise as John says.
Dare I say it is mostly Spaniel folk that like to get in a "rabbit pen"!