Dynamics is really just a term that (generally, when talking to a drumner, at least) applies to utilising the full range of volume-levels. A ghost note is just a quiet note, so yes, a ghost note does use 'dynamics' by definition.
The problem you're getting with hitting the hi-hat lighter when you hit the bass drum lighter is really common and happens to everyone - your hi-hat hand becomes wedded to your bass drum foot in a weird way (I really noticed this when learning to play left-handed - it's hard to separate your hi-hat hand from your bass drum).
The best way to overcome it is to do some interpendence exercises that make you 'separate' (playing-wise) your limbs more than usual. My favourite is Herman Vogt's coordinated independence (available free in PDF format here: http://www.hvogt.de/drums/patterns.html ), which starts simply, and gradually adds complexity. It's easy to learn, and it's based on actual drum beats - so it's also fun to play, and you get a lot of new beat ideas from it.
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