You ooma has a 911 fused address, but it travels a random route that can change every second based on the winds of IP BGP4 routing, and hopefully gets to ooma's soft switch which then drive it to a 3rd party 911 gateway provider. They then drive it via ip to a local provider that actually has a gateway to your PSAP, and hopefully only one hop instead of some reseller who is buying from another source. And most of these are not top tier 5 9's reliable systems and likely have little surveillance or monitoring. The only time most IP systems know there is an issue is when someone complains about a failure.
Unfortunately even at federally mandated 99.999% availability for POTS 911 availability still leaves 6 minutes a year its not available. IP paths are tough to even maintain 99.95% availability and that comes up to over 4hr/yr, hopefully your emergency is not during one of them. Plus on POTS they have to prove it was available which is pretty straight forward with direct trunks. On IP they don't have to prove anything, and typically don't know anything other than the local link is up, and maybe that they can reach the gateway.
So this is a two edge sword, pots require monitoring, mandated maximum response time, and regulatory reporting of outages and unavailability. But this cost BIG money and makes you subjects to big fines, and the subscriber is going to have this cost built into their bill.