We are just finishing up our 4th KOA work kamper experience; we have enjoyed it for the most part. We have worked 15-20 hours for the site and minimum wage for any hours over.It seems most campgrounds don't give you a lot of paid hours.
As far as the $35 I feel it is helpful IF you plan to stick with working for KOA as it stores all your info and it is available for potential employers to find even if you do not send it to them but if you want a wider field I would go with another method of finding a job.