Exe files built with XE3 should run fine on windows 10. I tested Delphi 4, 5, 7, and XE4 applications on Windows 10. If there are any issues they will occur because of your specific application code, and not because XE3 apps would not run in general. Without testing your apps under Windows 10, you cannot be 100% sure they will run properly.
I am also using Delphi 7 and XE4 under Windows 10 without any issues. XE3 should run fine too.