I'd be wary of renting my skoolie (when I actually have one. . . )
I'm wary of rentals in general, especially because sometimes you don't get back the thing you rented out. Cars, tools, clothes - its the same all around. There are certain people that I'd pretty much hand over just about anything to - because I know I'll get it back in better shape, or if its something like a tool, and it breaks, they'll replace it. But that's a REALLY short list.
I wouldn't want to risk all the time and sweat equity invested in a skoolie for a little cash for a rental. I'm also not sure I'd trust my build quality to hold up - I'm not saying that I'm a bad builder, but a lot of people on here build things their own way, with their own design in mind - so a random stranger might not be able to figure out how to fix it.
Insurance is also questionable enough - the last thing I'd want to do is have someone get into an accident, and have the insurance company find out I was using it for commercial purposes - and deny a claim.
Nothing wrong with the skoolie conversion companies, you're just trading your time, labor, and sweat, by paying someone else to do it for you.