re: radiant floors and dinning table

The wood will move seasonally wherever you put it, so the connection to the base should allow for the natural expansion/contraction of the top.
Radiant heat is less drying than forced air, so it won’t change the humidity beyond what occurs with the normal seasonal fluctuation.
If the top already has a crack, it may continue to open up with the normal seasonal movement unless you stabilize it with bowties. Most of my furniture has live edge slabs incorporated into it, and I have radiant heat, and I haven’t had any problems.