I looked up Utah statutes out of curiosity, and it appears that authorities can test CDL holders any time without probable cause, and being unconscious (or dead) is irrelevant.
This is the basis for the cop obtaining blood here. The nurse cites hospital rules that pertain to a person suspected by the police of being under the influence. But the semi driver was not suspected, nor was he being placed under arrest for anything. So it seems those rules wouldn't be relevant at all here. The Semi driver had a CDL and is subject to check anytime by authorities even if unconscious.
When the cop snaps, goes all Andy Sipowicz on her, and tells her she is under arrest, she begins backing away from him, yelling "No!" and then "I'm being assaulted", etc. All of which is completely understandable and entirely the cops fault.
There is evidence to support the cop's statement that he was instructed by his superior to arrest anyone who stopped him from obtaining the sample, so it's possible (probable) he may also have felt he was just doing his job. But if it is going to be done, we've seem it correctly and calmly done a million times. "Ma'am, at this time I'm going to inform you that you are being placed under arrest for obstruction"... and so on. All done very calmly and reasonably.
The fact that the cop may very well have been legally correct doesn't justify his handling of this situation in any way, shape, or form and he should be severley disciplined, IMO.