Sorry for the post delay, but I just noticed it now.
TheMaster's
I met these guys by joining a random VS server and we played VERY WELL together. So well that we added each other to our friends list and have been playing VS with each other for several weeks now. These guys play as a team which I VERY MUCH like since it is a rare thing in L4D VS mode and we have not lost a game yet in VS when we play together. Every time I play with them I can tell you that we do not cheat and that game we played was the FIRST time we turned on sv_cheats ONLY for the purpose of playing Dead Air on VS, which you cannot play unless sv_cheats is on.
To answer your question about the Tank in the parking garage, TheMaster spawned the tank to help out your team because he felt that the AI Director wasn't helping your team out enough since we all had basically full health AND unused medkits. As far as I know, this was the ONLY situation where he "Cheated," but it was to help your team out since the game felt unbalanced. As for the many hunters you saw, no exploit was used, just teamwork. As I said in the last paragraph, we play together often now and communicate A LOT on the mic to let each other know when a smoker has pulled someone and when a hunter needs to attack, etc.
I was specing everyone at different times when I'm dead since there is a 20sec respawn time and I did not notice anything unusual going on.
That video you posted shows a glitch that I've seen other people use and it is VERY unsettling. I know those 2 guys don't use it because one game we played together someone used it against us and we STILL played the game out the legit way for several more minutes before finally banning the exploiters from the server. In addition, they were even complaining about several exploits that your team used (skipping portions of the map by jumping on things, etc) because they wanted to game to be played in a normal and clean manner. I personally didn't mind since when I play with you guys on EXPERT MODE we use the easiest way to win, but that just goes to show how clean they actually are. They mentioned it to your team after you did them, so I think you may recall. But once again, these guys are as clean of players as any GC member.
Also, that was our first time playing that map on VS. TheMaster has the cfg file to play the 2 maps that the game won't allow so perhaps the "fast moving glitch" was a bug from the game or perhaps it was since we technically aren't supposed to be playing that map.