What safety concerns are there for discharging capacitors directly through a short?
You're going to run into two dangers doing this.

1) The spark. Depending on the voltage on your caps, there could be a very large spark when you suddenly short the terminals. That will need to be contained. Repeated applications could lead to damage of the terminals or the discharge bars. I'd recommend using a contactor to make the actual connection. Depending on the voltages and currents, that could get pricy.

2) The current. Again depending on the voltage, the ESR of the cap, and the resistance of the discharge path, you could be talking about kiloamps of current. It's a very short pulse, which thick wire and bar and good connections should be able to handle, but the instantaneous thermals might damage the capacitor. You should consult the datasheet, or else the manufacturer, to find out the instantaneous pulse current the cap can supply. My guess is that most aluminum capacitors wouldn't support that kind of behavior for large numbers of repetitions. And if they failed after a few shots, it might be pretty sudden.

As for maximizing the current and mimimizing the power loss, you'll want low ESR caps, lots of them, in parallel. Without specs it's impossible to make more concrete recommendations.