I'm sure they would hold up to 150ish deg water. Most of those type barrels are pretty thick. The only concern would be any compounds "leeching" into the wort because of the heat. I know people do ferment in containers like those, but I don't know about mashing. Great prices on them though.
Screw it, Lets brew it
Primary 1- BM's Cream of three crops.
Primary 2- Paleface Scalper
Primary 3- Monks Reward (Kreuzberg)
Kegged - Honey Badger, Heady topper clone 1, Indian Paleface Scalper
Bottled- Skeptical Dog winter Lager, Hell's Belgian, Old Dutch Hiefer Hefe,Aphlewein, Chocolate Thunder porter, Jacked up lantern