Of course, but the problem is that the enemy radar may be more powerful than your jammer, therefore you can still get shot at, but as a whole yes, it does it's job, and allows you to get to places defended by SAMs. Matter of fact once I reconfigured my stick with more countermeasure focus, my survival rate of course went up. Problem is though, even if your jammer is very strong, there is what is called "burn through", i.e. the SAM radar overpowers your jammer, and then can still lock on you. Fact is there's a ton of online references that deal with it, since in some cases the tactics used in real life work in the game, to a degree.
So basically you get a hit or miss proposition when dealing with jamming, SAM capabilities, etc.