Like all jobs, you never know until you start the job and see the lay of the land.
We have considered it. We were hiking up to the Gila Cliff Dwellins in NM and met a guide when we got there. (Amazingly they let you go thru the dwellings unescorted.
The guide was a workamper of sorts. He was retired and he and his wife had signed on for the winter season. In return they each got $10 an hour, he guided people up to the ruins (though you could go alone) and she worked in the visitors center. In addition they got their camping free, in a private campground including propane and electricity.
This NP is in a very rural but beautiful part of NM and I found it very enticing. We plan to return to this park this fall for another visit. I suspect that with all the parks their are many opportunities like this though I must say I don'tnow the process for applying.
I have noticed that state parks in Alaska seem to be looking for summer hosts as well.