Those stands will cope with the weight of a UPS up to about 1000VA - We have some of those stands under Dell servers and they just cope although I'd not want to put too much more weight on them.
Unfortunately, anything on the floor is vulnerable to flood damage so raising everything is sensible - even if you want to make it an 'art installation' and use a pair of bricks!
Do bear in mind too that any flood makes the atmosphere damp - someone I know had a flood and the bottom of a server's tower case got a bit wet and his server died shortly afterwards because the PSU started fizzing and took out the motherboard - it might have been coincidence, but I suspect it may have been due to moisture/condensation. Any IT kit left in a damp room needs thorough inspection and drying out before thinking about reapplying power.
Tip: If you have an APC BackUPS or SmartUPS, they have some bolt threads that stick out through the bottom of the case and they are really good at scratching anything they are placed on - especially PC cases.