The power supply itself will not know if the feed is on a UPS or not.
For the power spike issue, since the feed goes to both power supplies then a spike could potentially take out both supplies. If you lost power on the street side then it would affect both power supplies and the chassis may not have enough power. If the UPS can only supply one power supply total then I would put both feeds from the UPS into one power supply.
In general a power spike should take out the expendable power supply before the rest of the components in the chassis.
