No, USB-A on omnia is USB 3.0. So unless you buy a crappy adapter, it will run on 5 Gbps USB 3. Not the 10 or 20 Gbps the drives might use on a USB-C connection, but definitely not USB 2.0 speeds.
The major problem could be power supply to the drives. There is an internal header providing 5V and 12V that is meant to be used for external drives. It seems you can draw at least 4A from the 5V line (Omnia +5V0 output max current). Or, if your drives aren’t too hungry, each of the USB ports should provide 2.5 A. So you should probably check the specs of the drives you’re thinking of and match them against these power options.