Pufferpunk -- A healthy horseshoe crab is a newly imported horseshoe crab that's been properly cared for. They're tough animals, but in ordinary aquaria, they quickly starve. So if it was me, I'd gamble on getting a new specimen, considering "settling in" less of a problem than starvation. Wet Web Media has a pretty good summary of the North American species, Limulus polyphemus, but I'd add that that animal is a temperate to subtropical species and so perhaps not a perfect addition to a tropical aquarium. Th Asian species we've been discussing here is a tropical, and hence pre-adapted to high temperatures.
Cheers,
Neale