Also as
madphysicist mentions you are just paying to have access to the site and contact the hosts, workaway doesn't go and check the hosts out etc. Many though do have positive feedback / reviews left by people, and you can contact the people that left those reviews for more info if you wish as well.
I also ran into another person who had done workaway at other locations in Japan and he said he hadn't at any stage come across a bad host. I think in Japan at least there seems to be a good track record for hosts.
From the UK I checked it out beforehand and was able to go on a standard tourist visa, but by all means double check incase anything has changed. Everyone else I met who was also doing workaway were also on standard tourist visas.