Its a hoff-stevens keg, and they have pretty limited use because of the bung hole in the side of it. I guess you can weld the hole shut, but what would be the point of welding the sheet on the bottom?
The other limiting factor is that it doesn't have handles like Sanke's do. You could weld/bolt handles, but between that and welding over the bung hole....most people feel that they get to be more trouble than they are worth.
That being said, if you can work around those issues, no reason why is couldn't be used to hold hot liquor, mash/boil in, etc.