Is it true that salt can be used to put a slip resistant surface in fresh concrete?
I don't think you'd want to use salt for a couple of reasons:
Instead, use one of the polymer grip additives designed for this purpose - they can be very cheap, and some are transparent so do not affect the appearance of the concrete.
An example - I haven't used this one, but there are many available.
Many people seem to assume Jack was talking about mixing salt into the concrete but I believe he had been told about salt finished concrete. I used this in my new driveway and love the look but of course it is a matter of taste and style.
If slip resistant is the most important parameter, I would recommend a broom finish.