Time to bring out the DVD again I guess but IIRC it had more to do with the volatility (?) of the toxic compounds. Direct contact was not the issue, toxicity was carried with the water vapor.
If that is the case then using toxic plants in a solar still would not render the product safe to drink.

Perhaps filtering the product thru a charcoal water filter might work but i don't think I want to be the one testing it.
How often will you find ONLY toxic plants to use in your water recovery/distillation process?