Yeah, that should work. You can try downloading the launcher at the end of the post below, and unpack it in "/Applications/Zenimax Online" (create the folder if it isn't there). Then run it directly (you may be able to ignore all the other stuff in that post). For whatever reason I've had to do that before when setup wouldn't run for me.
https://forums.elderscrollsonline.com/en/discussion/284435/how-to-install-the-game-on-an-imac-5k-guide
What I did was create a "Zenimax Online" folder on an external drive, and then put an alias to it in "Applications" (so "/Applications/Zenimax Online" is an alias to the folder on the external drive). I put the launcher in that folder, and then ran it, and it installed into the external drive.