The evidence does show that people with disabilities are more likely to be self-employed and in the informal economy. My presumption is that it is because there are more barriers to formal employment. But of course simply being employed doesn’t mean that the quality of the work or the remuneration that you are getting is decent.
And I think the trends you mention have different impacts depending on the type of disability. As economies develop, work becomes less physical and more associated with constant learning. This makes it easier for people with physical disabilities and harder for those with intellectual disabilities.