Most of the time this is true, but strangely enough, you can use cheats in Grand Theft Auto 3 and it does not stop trophies from being unlocked.
This means you can spawn a rhino if you are having a hard time with a car mission, give yourself guns or health during a tough mission and it will not block any of the game's trophies.
This has been tested several times. I was personally able to perform the money cheat and I got the trophy for getting $1 million.
Cheats can have an effect on your total criminal rating, so use them sparingly if you have yet to get this trophy and intend on going for the platinum.