One thing to try is to let the cooked rice rest for a while.
My rice cooker's pot is non-Teflon and scratched, but I've found that if I remove it from the heating element and let it rest 15-30 minutes, there is virtually no sticking.
If I try to remove the rice immediately, there is significant sticking.
cooking.stackexchange.com/users/1092/erichui
I have been using Rick cooker for my whole life.
The simple answer I can give you is the problem of your rice cooker.
There are older models of rice cooker that sticks a lot and there is very little you can do about it.
It happened to me when I was little that some of the rice cookers just did that regardless of what we did.
The newer models won't do it unless inside it's scrated.
The Japanese brand rice cookers are very reliable, so you won't have problem like this.
I don't recommend you putting oil in your rice as I don't think it's an healthy option.
If there is no obvious scratches inside your rice cooker, then I think it's time to get a better rice cooker.
cooking.stackexchange.com/users/2951/Foodrules 
In my experience, it has little to do with your rice cooker model, the amount of water
(so long as it's reasonable i.e. not extremely scarce), or adding oil whatsoever (frankly, greasy white rice sounds pretty disgusting to me).
As a red-blooded Asian who loves rice and have been cooking it all my life, in various rice cooker models, using various types of rice, I used to have this problem when I was a wee beginner but eventually figured out a method to eliminate that stubborn crust:
The key is to let your rice rest for awhile after it's cooked.
When the rice cooker tab pops up to indicate your rice is done, do not immediately open the lid.
Instead, let it simmer down for a minute or two, allowing all those boiled water bubbles to settle.
Following this, open the lid
(I usually pop the cable off the socket for good measure) and let the rice steam out until cooled to your taste.
I personally leave it for five to ten minutes, and that results in just the right level of rice warmth for me, which is on the cooler side.
Your mileage may vary so test this out with different times to find a temperature that suits your liking.
And If you want to reheat the rice, it should be fine by now to simply pop the setting back on to "warm".
Voila--no more crusting on the pan.
Take into account that rice is sticky by nature, and a small amount of sticking on the pan is inevitable, but this should work to reduce that overall layer of crusting.
This is my way to prevent a hard crust on the bottom of the rice cooker pan.
I'm sure others have other ways that have been proven to work, but this one works great for me.
Note: this works for white rice in general, which is the most common and the type I'm assuming the asker was talking about.
Other types such as red or black rice would require more water and tend to crust more around the top, I have yet to successfully handle those.
cooking.stackexchange.com/users/50370/rice cooker
My mother came up with a simple solution - add a capful of oil (she recommended corn oil) to the rice recipe.
This time around the rice scooped right out perfectly.
cooking.stackexchange.com/users/2092/Jorge Castro
There are many factors at play here.
My experience is: The right ricemaker makes a huge difference.
A heavy pot (to better distribute heat) goes a long way to prevent sticking.
Many ricemakers go into "keep warm" mode upon completion.
When the rice is cooked, unplug the pot and let it sit without any additional heat added.
Make sure you stir the rice and water before starting to cook.
Just putting in rice and pouring in water (without stirring) tends to cause sticking.
Stay clear of "quick cook" mode which I believe uses a higher heat setting.
Go for a low temperature over a longer period of time.
cooking.stackexchange.com/users/68703/Kevin
Instead of putting 1 capful of oil to the rice, why not brush the pot bottom with oil before putting in the cleansed rice and water.
Try this out.
cooking.stackexchange.com/users/25408/meiissa
There is another good idea.
You can keep another vessel inside the rice cooker vessel.
But don't forget to pour enough water surrounding the new vessel.
Now you can cook what ever you want on that in the inside vessel.
Only disadvantage is this will reduce the capacity of the rice cooker, which means inside a 2 L rice cooker, you can only place a vessel smaller than that.
cooking.stackexchange.com/users/40554/Ajitha
I have a  Cuisinart  dedicated rice cooker and I  love the benefits .  However I get a little bit of stickiness around the sides of the cooker. A friend recommends a capful of oil while cooking the rice to prevent it from sticking, but I am not sure if that's a good idea?  The rice is sticking to side of the pot itself but it doesn't get burnt per se, just enough to make clean up a hassle.
How do I prevent stickiness in a rice cooker?
cooking.stackexchange.com
<rice><rice-cooker>
cooking.stackexchange.com/questions/9552
cooking.stackexchange.com/users/2092/Jorge Castro
Some older models of rice cooker are more likely to stick, and iti s difficult to prevent this. Try adding a capful of oil or brushing the bottom with oil before adding the rice and water, and make sure you stir before starting to cook. When the cooking is finished, leave the rice to rest for a while. Make sure you rest the rice before serving it. You can also try adding a little oil to the rice.
Stir the rice and water before cooking and let the rice rest before serving. Older models of rice cooker can have this problem. Add some oil to the rice.