Arc welding near LEDs. is this a terrible idea?
Arc welding uses high current not high voltages, however those high currents, 100s of amps, can induce high voltages in the wires of your LED array. Unfortunately, even if you clamp a work lead on either side of the weld spot, a considerable amount of current will still flow through the metal frame, which will induce currents in the LED wiring.

As such, I think you would be better not arc welding the frame back together. You would be better to use oxyacetylene welding, or any other non-electrical method instead.