I can't say I know what sort of robots these are (Military? Mining? Slavers?) I'd imagine that if they lasted this long, they'd be fairly resistant against harm. Kuhaku and Gren needed to combo-wombo to take them out, and I bet the boss would be even more durable. While probably not immune to electricity per say, maybe the EMP idea won't exactly work as well as planned. It might shut off some systems, but it doesn't need to use much fancy tech to slam it's giant fists on us.