So I did a bunch of testing with Reflect and can confirm what I thought was true, it does not act like a wall, teleporting characters will simply go through it like nothing.
I tested it out on Zelda, Shiek, Palutena, Metaknight and Greninja.
If you space it right Zelda, Shiek and Palutena will end their warp on the reflect you might be able to use this to ledge guard them but it's pretty perfect timing. Greninja is interesting in that from just the right distance if they use substitute you can punish it with reflect, using autoreticle (which why would you counter autoreticle but w/e) I was able to reflect afterwards and hit greninja out of the attack. Shadow sneak on the other hand is dangerous to try and reflect, if it's right at the end reflect will still work but they can continue going through and will punish it easily if you mistime it, it's simply a safer option to jab, smash or pretty much anything over using reflect in that situation.
Metaknights cape just goes through no matter what, the only way reflect will ever work is if the opponent spaces poorly in which case you would punish with a KO move or something else anyway.
Reflect is pretty gimmicky overall, you can punish shielding with it which is pretty dang awesome and maybe if you're lucky you can time it just right to knock someone just out of reach of the ledge.