If someone goes to the em claiming to have been sexual assaulted can the m.D. Determine physical "evidence of trauma"?

Yes, if is evidence. Md can recognize any cuts, tears or bruising. Should also use swabs to collect possible dna evidence from any semen present. Dna evidence can not be denied other than perpetrator claiming consensual sex.
Assult patterns. Bruising and other traumatic injury from sexual assault may cause specific patterns that able to to recognized by a medical professional.