Probably, I don't see a reason why it wouldn't work. But, the PSoC 4 might have difficulty processing the data from the serial port effectively depending on what you are trying to achieve
I need only send SMS.
For work properly MCU must be as USB master because 3G dongle is USB slave.
How to check it ?
Simple text interfacing will work just fine for USB interfacing. Try looking at these example projects for USB: USB Full-Speed, Low-Speed Code Examples (The ones near the bottom will have USB examples)
As you know that Cypress USB-serial product could work as SPI master whereas PSOC4 could work as SPI slave.
You could send text through the API provided by Cypress to USB-serial and then the data could be received by PSOC4.
I think it is not a problem.
I waiting to dongle for test.
Wish you could succeed.