I have a coated chassis on my Morgan, admittedly it's not an MMC original but a Terry Foxen (GEE) replacement. It's 7 years old now and holding up very well, I keep it sprayed with Dynax S50. Terry doesn't recommend galvanising, and there's not much he doesn't know about Morgan chassis.
Most Morgans don't get used in foul weather much, and especially not when there's salt about on the roads, so an electrophoretic coating should stand up pretty well. The old enamel-painted chassis were ok even if not particularly cosseted, mine was 25 years old when I replaced it, and it wasn't completely knackered.
Which is a rather rambling way of saying that I wouldn't see it as a deal breaker. There are lots of other reasons not to buy a Morgan
