Agreed. DL was far and away the best Zombie type game I've played and the trainer was great. Take care to avoid any MP options and there shouldn't be any problems with VAC or bans.
As already answered by PM: This is not a single-player offline situation. We do not condone or support cheating in an online/multiplayer environment (which co-op actually is).
They removed the VAC ban ages ago for this title, so go nuts
So, I might be redundant, but just to double check: It's fine nowadays to go into singleplayer without pressing buttons, use the trainer for some money, turn the trainer off and join a friend in co-op to tailor the game a little?