Whats the difference between a paragliding rescue chute and a parachute?
Drawbacks of a skydiving emergency reserve parachute compared to a paragliding emergency parachute would likely include excess bulk and weight, and possibly a longer time to complete the opening sequence-- though perhaps the latter point would not apply to a parachute intended for BASE jumping.  If one has room for the skydiving emergency reserve parachute in their harness, and one is engaged in a high-risk style of flying such as aerobatics, it might make some sense to consider flying with it rather than a purpose-designed paragliding emergency parachute.  

For more see related answer Can a paraglider rescue chute and its pilot handle terminal velocity?

It sounds like you have a more than merely academic interest in this topic; if so I'm sure you'll do further research, and we'll look forward to seeing a detailed self-answer to one or both of these questions in the future.