Ask Aunt Marge!
While Harry's magic was involuntary, and it's not explicitly stated in canon, I would be willing to wager that some sort of engorgement magic was involved in blowing her up in Prisoner of Azkaban. She survived the engorgement, was properly punctured by the Accidental Magic Reversal Squad, her memory modified, and deemed fit to continue living her life as before by Cornelius Fudge.
Canon never implicitly states all the things that might happen when an engorgement charm is used on a human. We can deduce from Ron's comment about Hagrid is that it may be possible, at the very least, to do an engorgement charm on a half-human/half-giant. If this is possible, one would have to ask if it's Hagrid's giant blood that protects him from being injured or killed by the engorgement charm, or keeps the engorgement charm finite (i.e. Hagrid doesn't keep enlarging until he blows up!). Again, this is just an idea based on canon, as most examples of Engorgio are done on non-human subjects:
- The twins placed an Engorgement Charm on the Ton-Tongue Toffee that
they "accidentally" dropped in front of Dudley (GF4).
- Kevin, the little wizard boy in the World Cup campground, was casting
an Engorgement Spell (or something very similar) on a slug (GF7).
- Hermione suspected that Hagrid has used an Engorgement Charm on his
- The fake Moody used an Engorgement Charm on each of the three spiders
he had bought to class to demonstrate the Unforgivable Curses (GF14).
- Harry cast this on a spider to practice with his wand (DH20).
Thanks to the Harry Potter Lexicon (E Spells) for the above list.
Dudley Dursley's tongue didn't keep growing, although it got very long, after the twins fed him the tongue-ton toffee, so he didn't explode eventually, or die.
I conclude that engorgement charms can be used on humans, but with little harm done. Aunt Marge (I believe) and Dudley are all examples of humans surviving engorgement magic.