Doing tutorials for money in Zbrush is going to be a very risky business. Like Ambient has pointed out, Zscript’s are a big part of what Zbrush is, and it would be supremely easy for everyone to make a quick Zscript of whatever tutorial you are planning on making.
But Bill brings up a pretty good idea. If you could focus on something that is Project based, and not just a simple Zscript, that may have potential for working. You might have to think of ways to make your Zscripts only usable with your tutorials, like maybe having to have certain files in order to run the script. But it could be done, I think.
But in all reality, I don’t think it will be a very profitable business. Unless people cannot learn by watching Zscripts.