Safety of adding dried hot pepper to opened jar of pickles
This shouldn't be a safety concern.  Bacteria could certainly be introduced (if you use your hands to add the pepper or a cross-contaminated utensil), however, the acidic environment of the pickling liquid should keep any possible bacterial growth in check.  The other contaminant to consider would be botulism, but again, in a pickling environment (high acidity, high salt) this is not a concern.  So...make your pickles as spicy as you like.