A tip is for services, what you mean is a bribe - LOL!
It does work in many hotels, but not in WDW. In some hotels, you can ask the person that is checking you in if there is any suites available, tell him or her it is a special occasion of some kind, and shake a $100 into their hand and voila, you are in a grand suite. There are many codes they can use in the computer and put you into a great room.
However, WDW is different. This cannot be done. Most rooms are accounted for and I'm not sure if they CAN do it, without a good reason ie: the first room checked into that was reserved had a problem of some kind and an equivelent is not available.
As far as restaurants, money talks. It is true. For example: If you are going to the Cali Grill and you would like a table by the window, after giving your name, ask if there is a window table available and discretely give the person a $20, OR the person that seats you once in the restaurant upstairs. If there is more than 1 person there it can get tricky but men know how to handle this. Since window tables are not reserved, they are requested at check in....well someone has to get the window table. I was just using the CG for an example and in no way stating that this is done by the CM at the restaurant.
What you saw on TV about Las Vegas is true

WDW has a "tighter" hold on their hotel reservations. Comparing LV to WDW is like apples and oranges....but both are great fun.