It should be fine, just keep in mind that you are only going to get USB 2 speeds. If your TVs internal video player doesn't work see if Nova Video Player does.
Worst case just return the USB drive.
Are you certain that the tv can play files from the usb?
Sometimes Android TVs refuse to recognize a USB flash drive larger than a certain size. I tried to get mine to record TV (a build in feature). It would do so to an 8GB drive, but none of the many 16GB drives or bigger would be recognized.
It should be fine I've plenty of USB3.0 flash drives and use them in a manner of various USB2.0 and 3.0 ports.
The only difference is in a USB2.0 port it will have a slower read/write speed
I am not 100% sure about it, but I think USB 3.x backward compatibility to older major USB versions, all the way to 1, is mandated by the USB standard. It is technically possibly to create a USB3 only device, that wouldn't have the old D+/D- lines at all, buy i've seen MANY devices, including quite a few USB3 flash drives and external hard drives, and have yet to see one that can not be used on older USB ports.
3.0 is backwards compatible with 2.0.