Now my company are using crs112-8p-4s-in switch and apc bx700u-gr UPS.
Is it possible to connect serial port in switch with usb port in ups.

ups has usb b type male port.
Now I'm considering to use rj45 to usb adapter and then use usb a type to usb b type cable.
Is it possible? I really want to know about the possibility.

I'm almost certain it's not possible. Certainly not possible with passive adapters.

no, that will not work. You would need some device that converts serial over USB into normal serial port.
It can probably be done with with raspberryPI, but that's quite a overkill...
Maybe even some small microcontroller would do the job, I remember Atmel have tech-note how to do something like this on AVR (AVR280 USB Host CDC Demonstration), but I don't know about any ready to use project or device like this you could just buy and use.

Mikrotik continues not to provide USB ports on devices, even when CPU does have it, limiting the possibilities, which sucks...

No it won't work...