Some peanut hay is actual crop residue off peanut fields where actual "Planters Peanuts" are grown. Prennial Peanut hay is different entirely as it is actually a hay crop. Peanut hay is quite common in FL.
As to peanut hay not colicing a horse as easily, this is a forage test issue! Any hay with a high NDF (netural detergient fiber) will be prone to colic an animal. The higher the NDF of a particular hay, the slower the hay will ferment in the hind gut of the animal and thus the animal will be more prone to impaction colic. Bermuda hay is notorious for impaction colic, bermuda hay will run from 63 to 75 NDF whereas alfalfa will run from 38-60 NDF. Prennial Peanut will be somewhere in the middle of these two.