Can I pay a non-USA resident in stock?

A great deal depends upon the employment arrangement that will be (or was) in place with this "guy in Australia".

If there is some way in which your arrangement is deemed to fall within the scope of the Fair Work Act 2009 (the major legislation governing employment arrangements in Australia) then you cannot pay primarily in company stock.

If your guy is deemed to be an employee of your company then the Fair Work Act requires that he be paid certain amounts in Australian dollars.

The minimum payment is the relevant award wage for his classification if he is covered by an industrial award (most employees are). If he's not covered by an award, then the minimum payment that must be paid in AUD is the Federal Minimum Wage (but it's likely that you've contracted him at a higher rate than that).

Once you've covered off the required minimum payments in Australian Dollars, there's definitely scope to negotiate whether additional payments might be in stock, or US dollars, or anything else you might fancy.

On a lighter note, if the entity doing the employing is purely a US-based company, then it's unlikely that the Fair Work Act 2009 will apply. But the Act is intended to apply broadly to the majority of work undertaken in Australia, and there are penalties for not complying with requirements of the Act. If you have any doubts about whether your employment arrangement with your "guy" might by covered by the Act, then it's probably worth getting some legal advice from an Australian Workplace Relations lawyer.

ON THE OTHER HAND, if your "guy" is operating his own Australian business, and offers the services of his company to your company, then the sky is the limit. You can undertake a normal commercial negotiation between companies that sets out the services to be performed and the nature of the payment for those services.