I used to be an ambulance paramedic and at times covered both Luton and Stansted airports and so potentially could have been sent to a similar incident to this had it happened in the UK.
There certainly isn't any instruction to leave the treatment of the crew either to after the passengers have been cared for or for any accident investigation reasons.
Similarly that pilots on this forum shouldn't second guess what the flight crew involved in this accident did or didn't do, I can't comment on the actions of the rescue teams that attended this crash, but either the unfortunate co-pilot wasn't treated because he wasn't accessable or his injuries were so severe that other casualties that stood a better chance of survival took priority. Almost certainly in this case that rescuers just couldn't get to him.
In any mass-casualty situation the idea is to do the most good for the most people. That does mean that sometimes someone who is very severly injured with little chance of survival is passed over for those with lesser injuries. There is no point rescue personnel concentrating on one very badly injured person while five others with slightly less serious injuries slip away.
Certainly, whether a casualty is a crew member or passenger wouldn't enter into the the decision process.