So, I looked this up in my org. III undergrad text (Hoffman's Organic Chem). There he states that the interaction of a fluorine and a chlorine atom is the interaction of two p orbitals. However, he goes on to say that second row elements, such as silicon, phosphorus and sulfur can hybridize, but they don't have to (I would add chlorine to this list). The obvious question out of this statement is "When do second row elements hybridize?" I doubt that this is a yes or no answer, rather, I believe that a trend is likely to emerge, where a mixing of completely hybridized and not hybridized is likely to occur.
So, perhaps Chloromethane is tetrahedral sp3, but perhaps when bound to a different atom, say something with a larger radius from a larger row wouldn't require the hybridization to meet the Pauli exclusion principle.