I have two thoughts on this.
First and foremost, the danger inherent in storing diesel fuel in something that you or your mates are likely to up-end over your mouths when you're already tanked. Thankfully it's compression-ignition fuel so all you have to remember is DON'T FART.
Second - there are companies that manufacture diesel tanks from stainless, so I don't see why it'd be a problem. There are different grades of stainless steel of course, but I would imagine that kegs would be fine.
I'd paint the bloody things. Leave them in their original state and some bugger is likely to flog them and fit a tap at a party.