I don't see why it wouldn't work.

If you change focustarget to focusfocus(not sure if this works, untested), you could have your priest target your main's focus instead of their target. This is useful if you want them to heal while you are targeting an enemy, or if you want them to attack a different enemy that you are targeting. The only problem is figuring out how to set your focus. Technically you could do both, check your main's focus, and if it is dead/nonexistent, go by target. This might require another macro, but since you're binding them all to the same button it wouldn't matter unless you're at the macro limit.