OSX Link Aggregation for USB tether and WiFi?

There are options to networksetup to tell you whether the OS can bond a particular port or not. To do so, you need to hand it a "hardware port", which you can find by using:

networksetup -listallhardwareports

Each of those, in turn, can be queried using

networksetup -isbondsupported <HW Port Name>

Bonded networks are set up using the networksetup port name, not the kernel interface name, so if you were to bond two ethernet networks, you would do so like this:

networksetup -createBond myBondedNet 'Ethernet 1' 'Ethernet 2'

Querying the ports on my 2009 MacPro running 10.9, I find only the hardware ethernet ports to respond YES to the -isbondsupported inquiry.

Note that I didn't have to have the port operational in order for -isbondsupported to return YES, so in my case both of my ethernets responded YES even though only one is currently connected.