Hi solo1685,
It's never a bad idea to go back and get that diploma. As to whether a high school would accept IATA courses for credit, I am not aware of any that do so. However, it could be as simple as no one asking them. If I were you, I would contact the schools listed here (
http://www.bestonlinehighschools.com).
Also, I can tell you who I would approach. Look at the commercial programs like Keystone, Citizens, and others. They have a little more leeway in what is acceptable. But I think I would send an email to each. Should more than one school be able to help you, it could be useful to you to be able to compare programs.
As for the SATs being helpful, that would depend on your present age, your intended school, and the country in which you would like to go to college. If you let us know that, I may be able to be more helpful.
Tom Nixon