Watch hours gained thru Ad campaign will not be counted towards your 4000 watch hours.
So, if you creating an ad campaign just to promote your video and get the watch hour count, that wont work on your way.
Let me explain how to use ad campaign to your favor, to reap more views and subscribers.
Create video in parts, for example if you creating a video for 10 mins, break it into 3 parts.
Create ad campaign for 1st part, mention the highlights of the subsequent parts in first vide.
So, viewers watching watch your 1st part and will definitely watch the 2nd and 3rdd parts.
1st part video will drive organic views and watch hours for the next videos.
YouTube will consider 1-part video as ad campaign; other views are organic views.
Another way of getting organic view is, your next video will show in suggested videos list of the viewers who watched your video ads even though they haven’t subscribed to your channel.
If you run an ad campaign by incorporating these suggestions you can get views and subscribers quickly. we tech tube video.