Every time I play for a long time or really high, my lips start getting tired and I will either make vibrate them or play notes much lower than typical pedal tones into my trumpet to loosen them up - good or bad?

It works like a "lip" massage you loosen the muscle and vibrate them using other than their own tension. Keep the lips loose and close and push air out letting the lips vibrate with the moving air. When you go back to playing they will get tired faster than when you started though.