Need to power two or more UPSs to a common battery details follow)?
Sounds reasonably OK (without a detailed analysis).

The selected diode sounds very acceptable for the periods of use that you envisage.
 The battery will be essentially fully charged at all times so the under 1V drop should be acceptable.
 It would be possible to arrange a MOSFET as a "diode" so that there was even less forward drop, but it is probably not worth the additional complexity.

A caution: It is quite possible that individual UPS's will not tolerate well operation with no battery in charge mode. If they do not "see" a battery this may affect their ability to drop into operating mode when needed.

It may be better or necessary to disable the UPS charging circuitry in some manner in all but one UPS and to connect the systems directly with no diodes. 

If direct connection is not viable it may be possible to place a very small battery on the diode side of each non-charging UPS so that it sees this battery for charging purposes. This battery need not be in especially good condition. As soon as the UPS is loaded and the "local" battery voltage starts to drop the diode connected main battery will take up the load.