What foreign carriers can I use under the open skies agreement?
The best way to check this is to clarify with your institution's travel office (the one where you will submit the reimbursement).

However, my general understanding of the situation (From the days when I worked for the government) was that if there's a code-share between a US airline and the foreign airline you wish to use, they will generally be OK with that. The problem is if it's purely international, and there's no American airline that partners with them. Then you may run into some difficulty.