The fellow who I am subbing for has always heated his very Large cans of vegetables by peeling off the label and placing the can, unopened, into a pot of water, bringing it to a boil and then simmering (in the last hour of prep). He then opens the can slightly to drain part of the liquid off, pouring the remainder into a serving dish, which is covered with plastic to keep it Hot in case the Number One lion talks too long before sending people through the buffet.
A friend (whose daughter has Cordon Bleu training) insists that this is a dangerous way to heat canned vegetables. I can go either way with this, as I am not tall and muscular for dealing with the darn cans in the first place...but I am curious about the Food Safety issue.