Could any of this be reasonably heard from the US?
A little science is in order here to answer this question. For the most part, for the freq below 9 mhz, both the US and Australia will need to be in darkness to have a chance. The further east you go, the harder it's likely to be. Early morning in the east coast is a possibility, though a small one. The 9 and 10 mhz freq might be audible during daylight hours, but both the US and Australia would need to be in daylight for this to be possible.
Keep in mind that Australia is in their summer months; summer means more absorption of lower frequency HF, so even less signal than normal would be making it out. Adding to the difficulty is the type of antennas this service is likely using - verticals and low dipoles that would likely radiate in a pattern that would concentrate the signal in a range rather like an umbrella (yes, that's a huge oversimplification of NVIS) and probably using rather low power - 100 watts, certainly no more than 1kw - would add to the difficulty. It can be done - hams do it all the time using other kinds of antennas, but it's tough.
Bottom line, it's a tough catch to be sure, but with a good antenna and receiver, and awareness of the time differences between Australia and the US, it's possible. There are many utilities - some of which are linked in our wiki
- that can help you determine daylight/darkness paths between 2 points. Some receiver control software packages even have such a utility built-in. As I type this, GeoClock shows the west coast of the US and Australia are in darkness, so if I were trying for this, I'd likely start with the 7 mhz freqs and work down.
 Come to think of it, it's likely the base stations are running more than 1kw - I'm unfamiliar with Australian rules and regs. As a very rough comparison, when the ABC was still running regional HF stations, it was quite possible to hear them on 4, 6 and 9 mhz frequencies, even on the East Coast (during the right time of morning, of course). I very much doubt the base stations would be running more than these old ABC outlets did - 5 or 10kw. longreach?