Github Enterprise hasn't been faring too well at my work either this week. When you work on both open and closed source products and GH and GHE are both down, it leads to a very unproductive week.
GitHub Enterprise is confusingly both a "call us for pricing" tier of GitHub the website, and also an on-premise version of GitHub that you can run as an appliance in your own data centre. The first of those is ultimately just GitHub and so has the same outages, the second is running on your own hardware so (shouldn't be) tied to the website's availability.
There are multiple products: self-hosted (Enterprise Server) and hosted by GitHub (Enterprise Cloud). I don't know about uptime guarantees, but you can buy Premium or Premium Plus support with 30-minute SLA or a dedicated account manager.