They are taking DECs provided they have sufficient experience (many DECs have struggled in the past, many have failed.)
Broome is fine for the short term, it's quite a pleasant little town really, a good holiday destination. It's main problem is that it is so remote from anywhere else. E.g., it is a two day drive to the nearest capital city (Darwin.) If you like fishing and four-wheel-driving you'll be ok here. Other than that, it is bloody hot, doesn't get a lot of rain even in the wet season, has a nice beach and not much in the way of shopping. You will get good at buying off the internet.
The bonus is exactly as posted above. Stops after three years. No doubt the company will assess where the industry is at at that stage and decide whether further retention initiatives are required. Remember also that the bonus is subject to tax.
There is also a $10,000/year living allowance for Broome which is permanent.