Anyway, here are some general ideas about chords outside the key. Sometimes, a dominant chord outside of the key will be used to lead into another chord. An example would be the beginning of Cherokee in the key of Bb: Bbmaj Fm Bb7 Ebmaj. The Bb7 would be called a secondary dominant; it's a dominant chord, but its not the V of the key, in this case it's the I.
That would be an example in jazz. In rock, sometimes a chord progression will be entirely in major chords, whether or not they are in key. How many of you have seen a half diminished chord in rock? Look at punk songs especially for using entirely major chords.
In modal jazz, chords aren't really in progressions. You will often see one chord for 16 or more bars, so when the next chord comes, it need not relate to the first one and is often in an entirely different key. An example would be "So What" which has 2 chords, Dm and Ebm, that are clearly not in the same key.
As for your example, hey, if it sounds good, do it.
