While I don't believe the haxdash is quite as safe, I'm almost certain that the no impact land from ledge is either very weak or nonexistent in invincibility frames. Ganon has a different midair jump in PM that requires him to dip slightly lower for no impact land which loses a bunch of frames (
source). I'm not really positive about ledgedash/hax dash, but I don't think it's significant. Even in melee I think it was only a few frames of invincibility (
source). On the bright side, the midair jump increase lets ganon ledgehop onto stage with any aerial, which hugely bolsters his ability to get back on stage or edgeguard. Now that I think about it, I think what you are thinking of is actually ganon's invincible ledge stall (
source).
edit: also, off the top of my head, here are the chars ganon has significant chaingrabs on (may not be complete):
wario, bowser, yoshi???, dong, falcon, wolf, fox, falco, sheik, link, ganon, lucario, pika?, zard, ZSS, lucas, MK, D3, Ike, marth(ish), roy, rob???, snake, sonic???
cg to **** tier: bowser, wolf, fox, falco, sheik, lucas, mk?
cg hard: dong, falcon, link, zard, zss, d3, ganon, lucario
good cg: wario, yoshi, Ike, roy, rob?, sonic?, pika?
meh cg: marth, maybe some others
**** tier cg: ness, probably others.
obviously this list kind of sucks because there are a bunch I'm not sure of. The **** tier CGs like on ness last until like 15% max and don't really get you better followups anyway/you risk getting naired.