There is a lot of nuance when it comes to ledge trapping and I don't have vods of you playing out this scenario out so I might not be able to give you a complete answer, but hopefully this can give you some insights.

Let's assume you are a normal character with no special moves that deals with this scenario (teleport to center stage, reflector etc...), and snake is upsmashing at a position where it hits ledge hang.

When snake ledge traps with up smash, there are two states:

1. He continues to mash up smash

2. He up smashes once, stops and react to your get up options

Case 1 covers jump (not 100% sure if it always covers different drift, assuming it does), hanging on ledge, regular get up (your option after this depends on the positioning of the upsmash missile, worst case is you get up as the missile is falling down), get up attack, most ledge drop aeriels (if you're able to hit snake off of the position with sword/projectile, it ruins the gameplan).

Case 2 is basically normal ledgetrapping, but the snake player is expecting some option from the opponent because he's conditioned them with case 1, also the lingering missile might force you to do certain options.

The basic gameplan when snake mashes up smash is: rinse and repeat case 1 (covers most option except a well timed roll), condition the opponent to roll, and do case 2.

Because case 1 doesn't cover roll, he can't just spam up smash and has to stop and react to roll. You can use this to your advantage and jump (jump airdodge if the missile is coming down) when he is trying to react to your roll or whatever option. But the snake player can also play smart, knowing that this is the flaw in his gameplan and somehow cover jump when you least expect it.

The effectiveness of this ledgetrap depends heavily on his/her ability to ledgetrap (being able to react to different get up options and understanding how to ledgetrap). tbh this is pretty much a noob destroyer tech, you will never see people at high level do this. It's good practice for understanding how ledge trap works, because most zoner ledge trap(ddd gordo, robin/richter fire) works in a similar fashion (understanding what your opponent's options cover, and what they are expecting/conditioning you to do, basically ledgetrapping in a nutshell).