Is salt (Iodine) ever recommended to patients undergoing cancer therapy?

You're mixing up two different things. Iodine 136 is used to treat thyroid cancer, because thyroid tissue accumulates iodine. It kills the cancer cells because it is radioactive, not because of the chemical nature of iodine. Salt is iodized because some people have thyroid glands that do not process iodine normally, or live in areas where there is no regular source of iodine in their food. Before salt was iodized, it was common in people who lived at a distance from any ocean to develop enlarged thyroid glands, called goiters.

Poor nutrition is probably the origin of many thyroid problems (including low thyroid), and rich nutrition is vital to reversing them, or at least to prevent further decline. Learn here https://tr.im/JcqX2

Healthy thyroid function depends on a range of nutrients, especially selenium, folic acid, and iodine. Since most people cannot optimize levels of these nutrients through diet alone, a medical–grade supplement is vital. Of course, supplements should be used to complement, not substitute, for a balanced diet.

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No, it's not. For one thing, table salt isn't iodine-- it just contains a trace of iodine. For another, non-radioactive iodine doesn't treat any cancer.

It's used in some thyroid conditions, including cancer. It's only limited for a short period of time in some of those treatments. Otherwise, it'a non issue...obviously..