I've skied Corbet's when it was what seemed like a million foot drop onto a hardpack crater (80/81), and I've also skied it when you cold make a single check turn into it (81/82 IIRC). Of course it's dependent on total snowfall, but also wind patterns, the mood of Mother Nature, etc. You just gotta go look over the edge. It's not like you waste a run doing so. About 45 degrees.
All of that is dead on except the 45 degrees. Once you've done the drop, the remainder of the skiing is 39 or 40 degrees plus-or-minus a degree or two.
@Bob Peters would be the go-to guy on this since it's been a long time since I went in March, but as a kid my folks used to drag me from MN to JH the last week of March (lucky, I know!). I recall skiing both powder, and refrozen melt so hard that we saw a mama moose run across the slope with her baby right under the Casper lift. That was a two run day.
I have to say that although JH is my spiritual skiing home, I'd personally pick another spot for a late March trip, although you never know when you'll hit the perfect corn week!