I don't think using the Crusher Glitch to make the Ambulance a Ghost to complete Paramedics is even easy. Too much time is wasted when you go into Blue Hell and re-spawn on land.
It's actually easier just doing this right when the game loads up on a brand new save file in Portland. I like Portland the most and know the locations very well. I remember in my first playthrough to 100%, the Paramedics were so bad. I was younger, more impulsive, didn't think as an adult, etc...And I remember it took so many attempts and like 5-6 hours to finally pass it.
Now I try to stay calm, strategically decide who to get first, second, third, last, etc...I just finished my second playthrough of GTA III to 100% with 7 proof vehicles about 3-4 weeks ago, so it's fresh in my mind. I passed Paramedics on my 4th attempt. 2 of those attempts resulted in only getting to Level 4, so I didn't waste much time. My third attempt, however, I got to Level 10 or 11 and then failed. But on my 4th attempt I did it very easily.
Problem with Paramedics in GTA III is the time limit and also Gangs (if you do the story before Paramedics). So it's best to just do it first thing and get this annoying nonsense out of the way. Other than some of the Rampages in GTA III, it's the hardest thing in the game for 100%. No other GTA game is like this. I just finished Level 15 yesterday on VCS for Paramedics and did it first try, so easy. Same for VC, SA, and LCS. It's all easy except GTA III. Sometimes they give you like 15 seconds and the patient is far away in GTA III. I don't understand the time limit they give. It doesn't make sense, imo.