There is a reason OMV doesn't let you include USB devices in a raid array - you shouldn't do it. The hat (i have one) doesn't do magical things to make it good for a raid array.
Thanks for the reply. OMV doesn't appear to be what I need if it cant run raid on this device. Since the device does support software raid 0/1/5 per the manufacturer, I guess I'll be forced to do it manually. Thanks for the info.