Some of this depends on how the players build their characters.
With the generic classes, you can mostly mimic the fighter, rogue, sorcerer and cleric with warrior, expert, spellcaster (arcane) and spellcaster (divine) respectively. So in this respect, it could be ok to use out of the box adventures.
If the players build their characters as jacks of all trades (easy to do with the generic classes) they may be in trouble.
The cleric build via the spellcaster class compares the least favorably. d8 vs. d4, medium bab vs. poor bab and 2 good saves vs. 1 good save.
The upside to using generic classes is that the players have more latitude on how they build their characters. The spellcaster can take any spell so you could have a blaster type who knows a few healing spells or a healer type who can magic missile the enemy.
Given the weaker cleric role with the generic spellcaster, I'd adjust the encounters slightly lower.
It'll also depend on how well your players know the game. That impacts how you adjust an adventure whether using core classes or generic ones.
Thanks,
Rich