it is, and it’s rather simple to navigate between them. Bare in mind that your LH Status won’t get you into the Vienna Lounge, and you’d have to have Priority Pass or similar.

Head to the Help/Information desk at T1 Security and explain that your flight is from G gates but you’d like to use the Vienna lounge. They’ll then let you through the security check point.
When you’re finished in the lounge, you have two options to get to G gates:
1) follow the signs for F & G gates (come out of the Lounge’s lift and turn right) and head downstairs to use the shuttle bus. This will drop you after T3 Security, but before G Non-Schengen passport control. The bus runs approximately every 10 mins.
2) go towards D Passport Control (turn left out of the Lounge’s lift) and pass through the checkpoint. Turn immediately left and follow signs for G gates. You’ll get to a lift where you then will walk along a very long corridor directly above the Check-in floor. When you’re at the end, you’ve arrived in G gates Duty Free.

Either route can take approximately 15-20 minutes not including passport control. I tend to check how busy D Passport control is, and then make a decision as to whether to take the bus. You could have just missed the bus and then have to wait 10 mins. Definitely give yourself 30 mins just in case passport control is busy.