Yes yes and yes! If your brother wants to jam unplugged it can certainly be done.
So I went the opposite of most and began with ABG, specifically the Olympia version of Tacoma's Thunderchief. I used dunlop picks, heavy attack, and some form of phosphor bronzes (I usually stuck with Elixirs). I regularly jammed with two guitars and light percussion (e.g. djembe or the like, because those were cool twenty years ago), everyone was unplugged and we could all hear each other fine. I was chasing the Brian Ritchie/Violent Femmes tone, he played an Ernie Ball Earthwood (massive bass!).
I do agree though that the right bass makes a huge difference here-- I tried a lot before I found the Tacoma/Olympia. The larger size of this and similar instruments makes unplugged jamming possible and not just frustrating.
I will say that after getting an electric, I realized that the technique I had developed on the ABG was all wrong for electric. I had/am having to relearn a lot. Also, just for fun, I put LaBella LTF's on the Olympia, and it has a nice sound, but very different and not nearly enough volume to go unplugged.