Sorry I've been out of the loop for sometime. Been busy with life and what not. I'll answer as best off the top of my head as I can.
Snip
Gato has many ways to AA his opponents of they jump in too much and are careless jumpers. Some examples: close stand

,

+

,

x 2 +

/

, his counter move (charge

,

+

),

;db

+

/

,

. The main thing to remember with Gato is to keep the opponent space in the range of all those normals/specials. Depending the situation is when you should use them. Yes JD does neglect a lot of these options but sooner or later they will get hit with something. Just mess around with them in a match. Also forgot to mention

+

actually beats out a lot of early jump in normals. Easy to link into his punch super afterwards.
As for Rock yes he is low tier. He has a lot of hard matches and his vitality doesn't help him much. He's like glass. Any character in TOP mode doing a combo on Rock is painful. Yes he does have some nice tick throw setups and a few nifty corner mixups with his teleport. Besides that you have to rely on using his kick super shine knuckle to punish openings when you get one. Also you don't have to chain from

+

his kick super. You can link it instead which is easier. You an also link from stand

. Almost forgot the mention. You don't have to do a full 360 input for 360 command grabs in MOTW. You only need to input:

,

/

+

.
Here are some common tick throw options players use with Rock:
-

+

kara 360 +

= This one is great cause it creates better range for the grab after a tick with a normal. You cancel the

+

somewhat late to create lower body invincibility in case they decide to go low on wake up.
-

+

+

kara 360 +

= This one is probably better because you are cancelling from a command normal with upper/mid invincibility. Again you can cancel it pretty late so you still get the invincibility frames, while creating some range.
Best examples of a good Rock player would be Wata. Here are a few of his many matches he has:
http://www.youtube.com/playlist?list=PLB409047018D65CAA&feature=view_allStill loves for Garou... Nocturnal what do you think abount dong? is him worth or i have to switch to someone else.
Dong is very good. He has a few match up issues but overall he's better than Jae options wise.
I could be totally off base here, but I always thought Kevin was limited to a certain extent. Whenever I had people pulling Kevin shenanigans, it was always the same ones with mostly the same setups. Compared to the Kim Bros, Gato, and Jenet, where you see a million different ways to approach using them and comboing like crazy, I always thought people would rather play high level players that were more fun. Correct me if I'm wrong.
Kevin can be nasty in the right hands. He Has multiple crossup options and along with a command grab it turns into a guessing game. Being able to combo into his super from any of his jumps in or dash ins makes him scary. Not to mention his meter building. Being able to guard crush you in the corner. Yes certain people do play him cookie cutter style but that wont get them far playing a good player. Like JT just posted JR is a great example of a smart Kevin player. In higher level play you have to be able to use all of Kevin's options to the fullest or you will get picked apart easy.
As for Tizoc. Yea he has the throw bug to worry about but I think he can be very strong with a good defensive style player. You have to remember the throw escape only works when they have meter or are in TOP mode. His main problem though is not having anything scary to punish openings with besides his command grabs. If you think about it all you have to really worry about are his normals and maybe his

+

/;c shenanigans. Every other special he has is slow on start up. I've won matches with Tizoc just using pokes so it's possible to win matches just very hard. I'm by no means a good Tizoc player but I know enough to use him effectively versus most of the cast. Best Tizoc players to watch are Yuji and Colossus.