Hustlers & APs use the terms interchangeably (because they never learned the correct usage).

One is clearly loitering and is that is the “catch-all” basis used by casinos to 86 hustlers.

The other one is checking machines or looking for visual clues to know when to play.

For example, I am walking around and observe that a bank of bonus slots are all at $3.75 (the top bet), then I am not going to check those machines. As a scavenger, I am looking for plays, opportunities for camouflage, taking on prop bets (aka gambling), etc. In essence, I am looking for machines to play and risking my money.

Some lazy, poor trailer trash who is waiting for over 30 minutes (had to move his seat a few times) waiting for a lady to tap out doesn’t realize the eye in the sky is taking notes and a few month later, the vulture gets 86’ed due to complaints. The vulture is too stupid (and/or ignorant) to realize casino patrons do complain to security, management, etc. After enough complaints, the casino just don’t want to deal with it anymore and out they go. Recall, everyone is being filmed or recorded once we are on the casino floor.

So, both words describe similar things and connote a common theme but are really different.

In the wild:
A vulture is waiting for some animal to die so the vulture gets a meal
A scavenger is look for a meal, but that meal could have been left there for a while.

My advice: Don’t be a vulture and piss off the yahoo’s or ploppies of the world. Scavenging is better because the machine is empty, no one is currently playing it, you don’t have to interact with yahoos and just go about your business.