Extending an iPhone Personal Hotspot?

NOTE: Though I'm using a Time Capsule here, I'm posting it in the AirPort Extreme group because I am given to understand that the TC's networking is basically an AE, and I'm not concerned with the TC-specific functions, like networked storage, for this scenario.

I'd like to use an old iPhone as the internet connection for a remote security camera. (I need to test the setup to see if the amount of traffic over the connection is too high to be practical on my data plan, but need to get it working first to run the test!)

The catch is, the hub for my security cams (Netgear Arlo) only supports Ethernet connections to the main network router:

(ISP) - (Modem/router) - [Ethernet] - (Arlo hub)

I set up a test to try this configuration:

(Mobile ISP) - (iPhone configured as Hotspot)[Wifi hotspot signal] - (TC configured as wireless network extender) - [Ethernet] - (Arlo hub)

A couple of notes about that:

• The Time Capsule had been working great in the wireless extender role, when it was receiving its signal from another Time Capsule that was connected to the internet via cable modem.
• For my current testing, I'm using a Mac in place of the Arlo hub, so that I can use Airport Utility to see what's going on with the network. I'm assuming that once I can get the Mac a solid internet connection, I can swap out the Arlo hub in its place.

I've set up that second physical configuration, and here's what AirPort utility on the Mac at the end of the pipe is showing me as a result (IUXTC orange status indicator flashing):

I tried fiddling with settings under Internet > Internet Options, but no help. (Changing IPv6 settings for example, lost the iPhone network and added a second orange item in Status at the bottom, for the network.)

Is the iPhone Hotspot network intrinsically different from a normal wifi network in ways that will prohibit extending it to a device like the TC? Or is there some deep settings I can change to get the internet connection to pass through?

I worship you as a Networking God if you have a definitive answer, especially if it's a way to get it to work :-)