Every job ad is different. Sometimes it'll be for 1 position, other times it is multiple positions. That's the unfortunate part of applying - you don't know. As for who puts up the job ad, that all depends on the size of the company. At a larger company, the staff budget is set on an annual basis with hiring requirements set by Flight Ops. Once a position is required, flight ops would advise HR who would be the ones who handle the recruiting process. At smaller companies, that may all be one person. I'd think Ornge would be the former.
With that said, Mrs.+TSRA works at a large corporate outfit and they just had a scenario almost what you describe - management hired a pilot, bypassing both HR and Flight Ops, because that pilot was friends with the CFO. Normal vetting was not done, and it turns out he was not a pilot the chief pilot would have hired. The pilot has since left the company. So yeah, that happens too, but I would imagine not at a company like Ornge.