Sorry for the long wait… I suspect a lot of people are glued to current events right now.
Anyway, I haven’t seen any chatter about the G6 firewall and would tend to think it’s because it’s not used in high numbers (if at all) with ClassicPress. That’s not to say it’s a bad idea – just, that nobody has really mentioned it. You might contact either BPS and/or Jeff to see if they have any insights. Since BPS has a firewall built in, it’s possible that G6 would be duplicating the same functionality needlessly. If you do find out, it would be awesome to hear back on your experience.
Not using G6 but using BPS (Pro) on all my ClassicPress sites and it works very well. BPSpro licence is a one-off and very reasonable price for unlimited sites - it may well be that BPSpro has all the functionality you need - also the BPSpro guy has answered a couple of my queries re it working with ClassicPress