I'm not familiar with the web site, but can give you some advise. Before responding, there are several different levels of "work camping" and knowing your level of interest will make a big difference in the way you search out such positions. With that said, are you looking for:
1 - Position for no pay like a camp host. Duties vary with a set number of required hours. In exchange you get a free campsite, and access to the the park amenities.
2 - Position for minimal pay. Part time work where duties vary depending upon skills (Sometimes no skill is required, or office, electrical or mechanical maintenance, domestic service, computer, some other professional or technical skill is needed). In exchange you get a free campsite, access to the park amenities, and a token salary (salaries can vary all over the charts, hourly or some other financial arrangement).
3 - Position for a permanent employee to live in the park. Everything covered in #2 above except the salary is a full time position like any other job (salary or hourly) but is a livable, sustainable income.
The next thing that you need to identify is what type of campground and location you are most interested in. State Park and State Historic Sites have multiple tiers of volunteer and employment opportunities and each state handles employment different.
Federal and Corp of Engineer volunteer and employment opportunities are handled on a different level.
EVERY private campground and campground organization establishes their own hiring process, and EVERY private campground is different. Organizations like KOA (Kampground of America) or 1000 Trails are nation wide organizations and their systems are somewhat coordinated. But the thousands and thousands of Mom-&-Pop campgrounds scattered through out the country are all independent. They may use some type of central organization (like the one you are referring to above) or they may be completely independent and advertise positions via Facebook, newspaper, or local word of mouth. EVERY one is different.
But, you need to identify what type of campground you want to give your time to, what your financial needs are, and your level of skill sets you can provide.
Here is the MOST important tip I can give you when it comes to seeking positions at ANY campground .... it's never about YOU. It's never about getting a free campsite. It's never about what the campground can do you you. It's not about getting a free hook-up campsite so you can survive the economy for X-number of months of your life. It's not about being located at a specific site so you have access to the surrounding area events, family, or available activities. No. When negotiation, you don't mention these things as your motivation for wanting to work there.
What you DO need to impress upon them is what YOU can offer to the park. Your services, you abilities, your talents, your willingness to work, your willingness to help make their park achieve a new level of success. You are there to promote their park. You are there to ensue every visitor to the park has a meaningful and rewarding camping experience, so rewarding to them they will want to come back and even bring others with them. You are there to serve their needs, to work THEIR agenda, to
If you put yourself on the back burner (how much money will I get, will I get a free campsite, how LITTLE do I have to work to get this), you will have good success. When the time comes up, you don't haggle over these issues... You either CAN accept their terms or you cannot. If you cannot, you simply say "Thank-you, but this will not work for me."
Even discussing the logistics of the campsite should not be a subject to debate over. Campgrounds have their established methods, geography, and they are offering the best they can to the prospective worker. You can either accept their terms or you cannot. But, it's not an issue to debate or you'll probably be rejected.
So, answer these questions first, which is it #1, #2, or #3 and what type of campground, location, and identify your skill set.
I do wish you great success.