After a lot of fiddling around, and trying out alternative shortcuts, I found a workaround! 
You can disable the dead keys through a program called Ukulele.
Instead of having ´ as a modifier key to allow ú, it now produces the ´ directly, which can be mapped in Dorico. After customizing the keyboard in Ukulele, in works natively in macOs, and I can easily switch between my new and old keyboard:
