Yes, pausing campaigns is appropriate under these circumstances, and a few hours isn’t going to hurt anything. Prolonged pausing for several days might cause some temporary performance issues.
But this is far better than letting campaigns run with the inability to reach a site. First, most of your ads will slowly get disapproved for not being able to reach the site. Second, you won’t be able to generate any conversions which will send a signal to automated bidding to start reducing bids and spending will decline as a result.
In other words, never send traffic to a site that’s offline.
We use Pingdom at my agency for all of our clients. Site goes down, we get an email and pause campaigns.