Yes, you can power up your Polyend Play instrument using the Poly 2 USB Host port. Just like any other USB-powered gear. Just make sure that the module is sufficiently powered.
There's a jumper switch on the back panel of the Poly 2. By default, the jumper is set to provide the 5V straight from the case AC adapter 5V bus if available. If there's no dedicated 5V bus in your case then the Host port may not be able to power up connected instruments sufficiently. In such a case, change the jumper switch position to provide power for the USB host port from the 12V bus.