No, you cannot take darvocet and ultram at the same time. Take one or the other, spacing approximately 4-6 hours between them whether you must take both. To take both at the same time could make you experience arrhythmia's, extreme nausea, vomiting and/or diarrhea and other unpleasant symptoms.
Ask your pharmacist! Darvon/Darvocet is a sched4 mild narcotic and is related to methadone. My experience with it is it works poor for any hurting over a 4-5 on a 10 scale. Ultram works better.