Street medicine is different than EMS.
A prime example of street medicine is the administration of buprenorphine in the field. Usually it's done by community paramedics and NPs/PAs. We haven't started a program yet for buprenorphine administration due to lack of follow-up arrangements, but we currently send a team to any overdose call within 72 hours. So if somebody ODs and calls 911 (whether or not they received naloxone), then a team consisting of a police officer, community paramedic, and a mental health specialist (currently we're using social workers) will go to the scene and/or residence of the patient and talk with them about treatment options. We plan to implement buprenorphine soon when we can get outpatient follow-up arranged.
Street medicine would be doing the follow-up at the patient's residence, at a rehab facility, or in the streets for homeless people.
Quite frankly, I do not think there is enough reason to do a fellowship with it. I imagine that it's just to pad a resume or to give a hospital some cheap labor to have a street program. It can easily be done with community paramedics and NPs/PAs.