Religion was a touchy subject back in Molière's day…but Molière himself didn't seem to have any qualms with making some jokes about it. The thing is, Molière's play Tartuffe doesn't make fun of religion: it makes fun of those who manipulate religion to get what they want – like, you know, Tartuffe. Still it's worth noting that there is no direct religious foil for Tartuffe; instead, Cléante has to do double duty as the voice of reason and the representative of true religious understanding. Through Cléante, Molière makes sure that everybody knows how foolish Orgon is acting, and lets them know that he knows what religion's all about.
Orgon is, ultimately, the most religious character in Tartuffe; though he does not understand many fundamental religious ideas, it is only his desire to learn and become more faithful that leads to trouble.
Molière has no need for a truly righteous foil for Tartuffe. One need only do the opposite of what Tartuffe does to act in a virtuous manner.