Is pedialyte good for you after excessive drinking? To prevent a bad hangover, and vomiting?

May help,not prevent. If you've been vomiting after excessive drinking pedialyte will help restore electrolytes you lost. It does nothing to prevent hangover/vomiting. Of course the best prevention is to not drink excessively, but if you do on occasion a good b-complex & vit c prior to drinking may help and homeopathic nux vomica 30c usually helps hangover symptoms. A hangover is your body telling you you're poisoned!
No. Electrolyte replacements won't decrease hangover or reduce vomiting consider drinking less at a time - enjoy your friends and social setting, but aim for fewer than 2-4 drinks each 2-4 hrs.