The d-amp in the vyvanse shouldn't cause any paradoxial reactions with the oxycodone. Since you are essentially speedballing, make sure you start off with a lower dose of oxy than is normal, and work your way up from there.
I wouldn't imagine it'd be dangerous, assuming you don't have any serious health problems. If you have experience with opiates then you should be fine. Just take a small dose (as above post describes) to be cautious.