...The only time I taped nonstealth with them, the wires were flopping all over the table - they're so light, there's no way they'll stay in one place! That seemed a bit dangerous with all the foot traffic, so even though I'm taping openly I still have to use stealth.
With those little DPAs 'tape openly' usually means pulling out the roll of tape and taping them down.
..reminder to keep st3lth talk st3lth. PM on its way in a few on some ways to use your DPAs that will cut down some chatter.
Putting the mikes behind the stage would, IMO, result in a far less balanced recording. There's only room for two people abreast, with the trumpet and sax players are up front, the drummer and guitarist behind them and the bassist in the back. Sometimes there's a keyboard player - he can't even fit on the stage and has to play right next to and in front of my table, along the wall.
Yeah, the brass players will certainly be more directional, but you may be surprised at what odd configurations will work. If the trumpet is really loud directly in front, the balance could even be better with him facing away. I bet you can hear the brass anywhere in that room. IMhO, brass tends to sound fine, sometimes better when it's deeper in the recording with some room 'verb on it than other stuff on-stage like the bass or the drums. If it sounds good behind the brass players on or behind the stage or against the wall, then putting mics there may be a good bet. That could be very 'low key' and out of the way as well. Worth a try I think.
It seems to me the most difficult aspect of this scenario will be getting good clear vocals. That will ultimately limit the choices of what works and what won't. I've had great results taping those little DPAs to a couple lengths of TIG welding rod (think nice, straight coat hanger wire) to form two super-thin antenna-like things that I could tape to the front of the stage and bend into position. Maybe make a nice arc that gets the mics a few feet up off the stage and a few feet or so in from the lip. If you use black tape it's nearly invisible from the crowd and no one but the band might know you're recording. That would get your gear out of the traffic too and avoid bodies walking between your mics and the band, no mater how protected they are. If this was instrumentals only, that would in fact be my first choice. Again this works to reduce the chatter by getting far enough away from the talkers and closer to the band so that the chatter is only heard between numbers.
If you try something like that and find the band sounds great, but it lacks the all important vocal clarity, you might tape those same little stalks to each side of the vocal monitor (if there is one) which is probably centered in the front of the stage facing up towards the singer, away from the crowd. The vocal monitor would then project up towards the backside of the omnidirectional mics. You'd need to bend the support wires to get an nice spacing for the mics and catch just the right amount and correct tone of the vocal, which will take some trial & error (you probably want to get them up and away from the face of the monitor a good bit), but if done right the vocals would be clear and centered in your recording.
Have fun with the options.