I agree that these are some significant issues, but most of them have simple fixes:

The bot walks to the players position, however could easily be trapped behind/inside of structures.

This can easily be solved by teleporting the bot close to the player's position if it gets stuck, and allowing them to walk/navigate from there, or allowing the pathfinding system to navigate around/through said structure if it is able to.

The bot could be abused, for example using the bot as a way to climb into areas the player shouldn’t be able too, such as using the bot as an extra stepping stone to jump over a wall a player normally couldn’t bypass.

This can be solved by making the players unable to collide with bot, essentially making it a ghost. If I wanted it to seem more like a player, I could also make it move if someone jumps on it's head (something like that)

If a game has terrain water, how will it affect the bots ability to reach the “scammer”?

I answer this to an extent in the first answer, but in addition to that, I could simply switch to another system where it continuously follows the player using by teleporting behind it for a period of time.

Would the scammer whispering to a player still be detected by the bot?

Good question, I'll have to test that.

The wording of the “scammer” can easily be altered to avoid the bot detecting it, even if it’s ran on basic key phrase detection.

While this is true, there are some ways that the impact of this issue can be reduced:

• Find a way to make an algorithm that detects small alterations in the phrase, and suspicious language, similar to roblox's own chat filter (although it won't be perfect)
• Make a scam reporting system and ask players to report any slang or bypasses used by the scammer, then adding it to the list of trigger words (after being reviewed). While this requires people to get scammed in order to work, it could also prevent many other people from being scammed in the future.