The 100 night is PiC but it is not a hard limit. The Islanders don't do night surveillance and an FO on the Dash is (obviously) not in command so doesn't require the night experience specifically.
Not quite having 100 hours night shouldn't be a valid reason to not apply. There is some flexibility there, whether they choose to use it is up to them I guess. You'd need to have other qualities that offset the night hours.
1500 total time is a hard limit (required by Coastwatch rather than SA) and is only relaxed if you have some previous coastwatch observer experience. I know of a couple of ex observers who ended up with flying jobs with SA.
A minor correction to Ops Normal's post, Surveillance Australia are no longer a subsidiary of National Jet. National Air Support is a sister company to National Jet (specialising in non RPT aviation contracts), SA is a subsidiary of NAS.
I'd agree that the Islander pilots are probably the best paid Bongo drivers in the universe, the Dash 8 pilots pay is not too far removed from what a Dash 8 RPT pilot gets.
The biggest gripe is the roster, it is not particularly stable, and due to the nature of the Coastwatch contract it will never be as stable as an RPT roster. But then RPT guys don't get to snot past a Cruise Liner at 200'/200kts.