Hey Mark,
I don’t think it makes sense to have an UPS on the machine but not on the spindle.
If you have the electricity fail totally, and the Onefinity/Masso will continue to run thanks to the UPS but the spindle will stop, you will break the bit and possbibly have more damage.
And if you want to power a spindle, it’s not a UPS you need but an engine-generator or emergency power system.