Final answer:
Yes, in music theory, using non-diatonic V and VII minor chords is permitted and is part of chromatic harmony, used for expressive purposes or to modulate to a different key.
Step-by-step explanation:
In music theory, you are indeed permitted to use V (dominant) and VII minor chords that are not diatonic to the key you are in. This practice is a part of chromatic harmony, where composers intentionally include chords or notes that are outside the key signature to achieve a specific effect or to modulate to a different key. For example, a minor V chord can be used in a major key to bring a more somber color to the music, while a VII minor chord may be used to lead to a modulation or to create tension that resolves differently than a diatonic VII diminished chord would.
While traditional diatonic harmony tends to stick to the seven chords (I, ii, iii, IV, V, vi, vii°) built on the seven scale degrees of a key, modern and classical composers alike frequently bend these 'rules' for expressive purposes. It's important to understand the conventions of diatonic harmony first, but once you do, you are encouraged to explore non-diatonic chords to expand your musical vocabulary.