Air Evac is the second largest operator. Air Methods is the largest. With over 300 bases they're over twice the size of Air Evac.
NVGs and radar altimeters are required on all Air Evac aircraft.
While the aircraft are not certified for IFR, they have the avionics / instrumentation to execute an IMC recovery.
Their pilots attend the IFR training in the sim semi-annually.
All companies get calls in bad weather. It's for the pilot to decide whether it meets their company mins and more importantly, personal mins. Some companies, including Air Evac, have pilots in the call center that must approve a flight in "yellow" weather. Of course all companies have the "3 to go, 1 to say no" policy. If someone in the crew turns it down, for weather, another company will be called.
These accidents in HEMS will continue to happen. It's the nature of the business. Nighttime accidents are disproportionately higher than daytime. You're sleeping, the phone rings and you have to make a quick, educated weather decision. Unfortunately you don't have a forecast or even current conditions for a road intersection. You can look at automated weather at airports around the area but you really don't know until you show up. Predicting wx in HEMS is an art form that only happens after getting to know local wx trends in your area. Even then, there are times wx bites you in the butt.
It's a common argument that is brought up by senior HEMS personnel a lot. That is we need dual pilot, dual eng, all NVG, all IFR fleet. I agree that would reduce accidents. Problem is no company can afford to equip their entire fleet like that. The little 206s and 407s cost far cheaper to purchase and operate than a dual EC-145. Unless these companies get some sort of supplement from the govt, they'll always have single eng, single pilot, VFR ships. Considering hundreds are saved annually over a ground ambulance, and it's a profitable business, HEMS will also always be around.