Yes, any workstation with MIDI out can be used with vA2.
You can use the sounds on the current WS with vA2.
vA2 can play ...Yamaha, Korg, Ketron and Roland styles.
Yes, vA2 is a PC application and that would be needed to run it.
If you added vA2 to your current arranger.....you would use the keyboard as input and the sound engine as output.
AND you can easily add other sound modules or software synthes too.

In most cases the buttons you use to run the arranger will NOT work for vA2 as most arrangers do not send MIDI messages when they are pressed. (That has been a complaint of mine for decades) But an easy thing to do is use a touch screen on the PC...or use a simple thing like Korg Kontrol 2 for the buttons.
There are many possibilities.

Lee