It depends on your monitoring needs and tech stack. New Relic has a pretty nifty monitoring product. Crashlytics is the go to for iOS apps. Testflight live has a crash monitoring and analytics product for iOS but its a bit clunky. GA you can also always view real time data and if nobody is onsite you know you have a problem (seemingly because its down). There's also free/cheaper more basic services that ping your web server to make sure your sites up and then notifies you if its down. The etsy team has a good bit of info on how they do analytics, monitoring and stats on their code is craft blog.

If you are trying to shift traffic from existing website to app use interstitial blocking pages. While somewhat annoying for users that just want to view content on the web they are very effective at directing traffic to apps. They're far more effective than the default iOS smart banners that are easily ignored. We found this for both iPhone & iPad use cases at Diapers.com (I also saw similar data from zappos) also once users dismiss interstitials or smart banner adding contextual links like "view XXXX page in the app" can prompt users when they're more committed as opposed to on first view.