I like to think of the harp in a different sense. Instead of thinking of it as an instrument native to Cb Major, with all the pedals pressed down, think of it as one in C major with all the pedals in the "middle" position.
The harp pedals can either be raised (#), resting (natural), or lowered (b). So, to play a C major scale, all the pedals would be in the middle position and the harp player could do it with ease.
Now, to play say, A C minor scale, we would have to lower the E, A, and B strings. To make it harmonic minor, just make the B natural.
To make things more complicated, the harp is all about enharmonic spelling to get what you want out of it. If you want to have a scale as such: C D E F G Gb A B C, you couldn't because to acheive the Gb you would either have to lower the G or raise the F, eliminating the ability to use whatever note you altered.
Chromaticism on the harp requires planning, but it can be done.
Now I do agree with Flint in that the harp naturally is a Cb Major instrument, but that complicated things a bit. A harp player reading a part will begin with the pedals all at middle position and adjust from there, not with them all pressed down. Hope that helps.