It all depends on the quality of the video content. Assuming that the video content is appealing AND the Google Ads (YouTube) video campaign is properly set up, then yes, it can boost a video by resulting in subscribers, likes, comments, shares.
Views from Google Ads (YouTube) video campaign will not count towards watch time.
Resultant effects of the engagements will have good benefits. Subscribers would watch past, future videos and all that would count towards watch time
Once again good results from Google Ads (YouTube) video campaign depends on on how appealing the video content is AND proper set up of the Google Ads (YouTube) video campaign.