Can the USB interface be used in real-time works
The concept of "real time" is a stretchable thing. If your controlled object is, say, a metallurgical oven, then, depending on the size of it the real control time may be from seconds to minutes or even hours. So you need to define more clearly what kind of sampling rate is sufficient to make a robust and stable control for your object. To determine which time-cycle do you need, you need careful analysis of dynamics and stability of your control loop. 

Now, the question is good, but it needs to be re-formulated. It should be something like, what is the overall latency of USB system, the time from issuing an API call from some software control algorithm, to actual change in some GPIO pins on the side of USB-connected device. The chain of events is long, it goes through API, several layers of drivers, filling various TRBs structures in main memory, then the hardware gets involved, ringing the bell register initiating DMA access by xHCI controller and streaming data across several elasticity buffers into actual USB PHY, then waiting for protocol response. And then something similar happens inside the USB device itself before actually toggling some GPIO pin. I don't know the answer to this question. But it is quite clear that the desirable sub-ms loop latency is impossible.