I have a 40 foot boat
with an encapsulated lead keel. Ran over an unmarked wreck and was hung up for a while, a few scratches only.
Another time I was following another boat that "knew" the way. I ended up knocking 6" of of some @%<?# %@#&% in some unamed tropical country at 4 knots. A few gouges only. The lesson being make sure he has more draft
than you and knows how to go slow.
From what I have seen on other boats that have hung up on reefs
I do not see a problem with an encapsulated keel as long as it isn't iron scraps. I do not like the idea of all that iron slowly expanding as it corrodes. Though to corrode it needs oxygen.