Truth be told, I was running sound, and it was at the KoAloha Anniversary party. Believe me, with my equipment, its only 8 channels, so the mixer was loaded (all of them had mics), and I'm nowhere near even entry level in running sound, but I did it as a favor to the Okami's (cuz they do so much for me). I've played Herb's instrument, and scoped out James Hill's as well as David's - the only guy I've seen stuff something inside the box is Tony Gamble.
John, I agree that playing into someone else's system, you're at the mercy of them, but from what I gather, the OP is using his own equipment at times, with a Baggs DI (with a notch filter). I'm assuming he's in control with most of the setup, so that's why I don't understand how feedback can occur with a UST, outside of the reasons already mentioned (which can be fixed by proper setup, or by changing the UST to a more `ukulele friendly one, if it is the UST causing the problem, which I doubt).
Aaron