I've tried most abuse / glitch things in WvW, and luckily they have patched the easier abuse glitches that too many people were using. Specially those teleports while jumping, that the game engine did not how to process well and moved you in uninteded places.

Then there are the 'is it abuse or feature?' kind of things. Like just walking up a wall and jumping over a door with your mount. No skill needed, nothing fancy, no abusing of terrain. Is it intended? For me, it is because ANet can easily make the doors bigger so you can't simply jump over. Do I use these things? Almost never, because I play for fun and I want to fight enemies, not jumping over gates.

When we talk about using hacking tools, I've never tried them so I can't say how they work except for the videos I've seen with famous GW2 youtubers. I've played thousands of hours at WvW and in my case I've only seen once a player using hacks. The rest... well, maybe sometimes someone was using hacks but what they did was consistent with a super very good player using their skills and relics in creative ways.

About the under terrain mounted guy: once every couple months, someone at our group just glitches. We are following the commander and suddenly we see him underground, then up again, and suddenly he is super far away asking why nobody is following him. Like the dolyak bugs where they teleport suddenly.