Can the DIV/GNSS antenna be used by connected PC or Raspberry Pi

Yes, you can. Its not too tough.

Instructions for enabling the GPS and installing gpsd (a deamon which creates a socket which other devices on the network can query) can be found in this post: [howto] GL-X3000 GPS configuration guide

There is a lot of app support for gpsd. But, if you want to write your own, have a look here for information on querying the socket: GPSD Client HOWTO.

My needs were much simpler (my X3000 is in my trailer and I wanted to track its location as I travel. I query/save GPS coordinantes every two hours, create a .gpx file every 12 hours and upload it to my VPS which already has a mapping interface and database), so I only enabled the GPS and directly query /dev/mhi_LOOPBACK directly. More information on the NMEA sentances in /dev/mhi_LOOPBACK can be found here: GPS Sentences | NMEA Sentences | GPGGA GPGLL GPVTG GPRMC.