Ok Here to make things easy for you.
PS3 games you can buy from anywhere in the world and ALL of them will work on your console.
After you buy games if you wish to buy some DLC for it, you have to buy it from the store of the country you bought the game for(It is usually region locked).
So you can buy a game from US and play it here, but if you buy the DLC(Like map or characters or extra mission) from India store, it might not work. To be sae you should buy it from the US store in this case.
Thumb rule if you get some game from outside india avoid buying DLC for it, and if you desperately need some DLC then buy that game from India.
As it stands games are pretty much cheaper or on Par with US here, it is just some exclusive games that you do not get there, so buy them there and do not buy DLC for them and you are good.