Controller Based WLANs

It is possible to use two 4G/3G dongles in the 70XX controllers as an uplink backup?

No, it is not possible to use two 4G/3G dongles in the Aruba 70xx series controller as an uplink backup. As per the design we can have a combination of wired and a cellular(3G/4G) modem as uplink backup.

Note: In the 7000 series controllers Aruba 7008 and Aruba 7010 are only two controller that supports 2 USB ports.