How to disable vibration for Timer alerts? In iOS Settings / Notifications, I can control whether alerts use vibration or sound or vibration-and-sound for Calendar, FaceTime, Mail, Messages, Phone, and Reminders apps. 

In Clock App / Alarm / Edit or Add Alarm / Sound, I control whether alarm-clock alerts use vibration or sound or vibration-and-sound. 

But I can't seem to have timer alerts (from Clock App / Timer) that are sound-only (no vibrate), without killing vibration for all apps. 

Or am I mistaken?
You are not mistaken; a very odd oversight on the part of Apple. Note that you can turn off "Vibrate on Silent" in sound settings and flip the side switch put your phone on Silent, which will disable that vibration and still make the sound (I believe). 

Also note that you can turn off vibration for alarms, but for some reason not for timers. My suggestion would be to download a different timer app from the app store if you want greater customizability.