Can I use a USB hub to attach more USB UPSes

Yes .... however in many cases there is some additional configuration required. 

1. If you are NOT connecting more than one USB UPS of the same model, and you are NOT connecting more than one USB UPS using the same driver name, no additional configuration is required. 
   
   
2. If you are connecting more than one USB UPS of differing models but that use the same driver, for each UPS using the same driver: 
   
   - Browse to the Opengear Management Console
   - Connect the UPS 
   - Click Status: Syslog
   - In Match Pattern, enter: .*USB device.*
   - Click Apply
   - Look for the last line similar to:
   <12>Oct 17 18:14:46 kernel: usb.c: USB device 2 (vend/prod 0x09ae/0x1007) is not claimed by any active driver.
   - Look for "vend/prod" and note the two numbers after 0x (in this example they are 09ae and 1007)
   - Click System: UPS Connections then Add UPS
   - Enter all details for this UPS as you regularly would
   - Under Driver Options click New Option
   - Under Option enter: vendorid
   - Under Argument enter the first of the two numbers from the Syslog page (in this example 09ae)
   - Under Argument enter: productid
   - Under Argument enter the second of the two numbers from the Syslog page (in this example 1007)
   - Click Apply
   
   
3. If you are connecting more than one USB UPS of the same model: 
   
   - Browse to the Opengear Management Console
   - Connect all the UPSes of the same model
   - Click Status: Syslog
   - In Match Pattern, enter: .*USB device.*
   - Click Apply
   - Look for lines similar to the one below, there will be one for each connected UPS:
   <12>Oct 17 18:14:46 kernel: usb.c: USB device 2 (vend/prod 0x09ae/0x1007) is not claimed by any active driver.
   - Look for "vend/prod" and note the two numbers after 0x, in this example they are 09ae and 1007
   - Login to the Opengear device's command line, e.g. by using SSH or by selecting Manage: Terminal from the Opengear Management Console in your browser
   - Enter the following command: cat /proc/bus/usb/devices
   - Look for lines similar to one below, where the Vendor and ProdID numbers match number you noted on the Syslog page (in this example 09ae and 1007)
   P: Vendor=09ae ProdID=1007 Rev=1.0
   - Under each of these lines, look for lines similar to below and note the number after the = sign, there will be one for each connected UPS:
   S: SerialNumber=c4912000
   - In the Opengear Management Console, click System: UPS Connections then Add UPS
   - Enter all details for this UPS as you regularly would
   - Under Driver Options click New Option
   - Under Option enter: serial
   - Under Argument enter the serial number you noted (in this example c4912000)
   - Click Apply
   - Repeat the Add UPS steps for each UPS of the same model