i guess you could yeah but a UPS also keeps all your shit alive and safe in the case of a power surge, and it gives you time to shutdown gracefully in the event of a sudden power cut
i dunno if you can get one that's rated high enough wattage for both computers, you'd probably need one each, both around maybe 700-800W, i can't really tell because i never have more than two drives in a computer and i don't buy extreme progamer video cards or CPUs