Hi atem, 

Yes, I would use the Page likes/page subscribes from Facebook Ads as a metric broken down by a campaign name to measure the follower count. You’ll find more information about these metrics from our connector documentation (I linked the relevant field). 

In case this query does not yield any meaningful results another approach I would try is breaking the “Actions” metric by Campaign name and action type. According to Facebook Ads documentation, you can track actions taken on your ad, Page, app or event after your ad was served to someone, even if they didn't click on it. The name of the action is “like” and you’ll find more information about the action type dimension here. When splitting by action type, make sure to fetch the Actions and actions- related metrics only as the other metrics like page subscribes cannot be broken down by action type. 

To summarize, I would play around with two different queries I’ve outlined to see what works best for you depending on your Facebook Ads setup. 

Let me know if that helped, I’d be curious to know!