Perhaps someone has done this but there is no direct connection on the flex1500. It may be possible to adapt the hardware in one way or another, but then the software would need to be adapted as well, to reflect this.
Yes you can connect the HR50 to the PC with a USB cable. The amp appears as a Comm Port in the system. In PowerSDR setup, enable CAT commands on that port and select "Enable Kenwood CAT Commands". Then the HR50 will track band/freq changes in PowerSDR.