If a miner can earn $170K or more by mining a block honestly, why would he try to scam someone for only $180K? That someone might later try to track him down to get revenge for the scam or be reported and wanted by the police.
I think the larger consideration is what if the scam doesn't work? Given how interconnected the network is today, and how quickly blocks spread, it is difficult to pull off. It is also trivial for the target to learn about chain split, and there are plenty of blockchain explorers and other entities out there which operate multiple nodes and can easily send alerts about chain split within a second or two of it happening. Given this, is it worth sacrificing a guaranteed $170k for a very small chance at $180k? Obviously not. You would need to be dealing with values which were multiple times higher than the current block reward, and as soon as you start talking about depositing 20+ BTC then no service in their right mind is going to accept only one confirmation.
Its only 7 million dollars and unless it was done back door and full remote the person would likely be caught.
The pool would effectively be committing suicide. No miner is going to continue to mine on a pool they know are attempt to pull off a scam and are sacrificing block rewards (i.e. the miner's income) for the pool's own personal profit.