What have you tried in RetroPie?

Does it show up when you type lsusb ?

For example, I get

Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp.
Bus 001 Device 004: ID 413c:2107 Dell Computer Corp.
Bus 001 Device 005: ID 0bda:8176 Realtek Semiconductor Corp. RTL8188CUS 802.11n WLAN Adapter
Bus 001 Device 006: ID 04d8:f673 Microchip Technology, Inc.
Bus 001 Device 007: ID 045e:0719 Microsoft Corp. Xbox 360 Wireless Adapter

Device 1, 2 and 3 are the USB controller on the Pi itself. 4 is a keyboard, 5 is a WiFi adapter. 6 is a custom device similar to how a Teensy should show up.

If you see the Teensy there, you can get further info with sudo lsusb -D /dev/bus/usb/001/006

If it is recognized by raspbian, it will show up under ls /dev/input as js[x]. If you see it there, try jstest /dev/input/js0, do you see the controls recognized?