if I wanted to use the verb nIH instead here, could I use the sentence beylI'vo' nIH?
The from of -vo' refers only to physical motion away from something. It doesn't refer to removing things from the possession of something else. Although the things you steal do move away from the bank, it's not the stealing that is happening from the bank.
beylI'Daq nIH vongwI' po'
The skilled hypnotist steals at the bank This says that the skilled hypnotist performs stealing, and the stealing happened at the bank.
beylI'Daq Huch nIH vongwI' po' 'ej beylI'vo' 'uch
The skilled hypnotist steals money at the bank and carries it away
(Literally, The skilled hypnotist steals money at the bank and carries it from the bank.)
It doesn't seem worth it to switch to nIH when Hej works so much better.
beylI' Hej vongwI' po' 'ej Huch nIH
The skilled hypnotist robs the bank and steals money.
In English, the word "rob" also implies the threat of violence, which might be a motivation to use "steal" if there was no threat. Is this not so in Klingon?
I'm pretty confident that the difference in Klingon is that the person or place being robbed is the object of Hej in Klingon and the thing being stolen is the object of nIH in Klingon. In fact, I'm pretty confident that outside of a legal context, that is also the general English lay use of the words "rob" and "steal".