G0-T0 has an answer for the Sith too.
HK-50s were made to be Jedi-killers, and were based off HK-47, who had countless force-sensitive kills. They're more than capable of taking down Sith.
But also, Myrkr.
1.) G0-T0 would know of this planet
Myrkr was discovered, or brought to center-stage, during the Mandalorian Wars, which happened extremely close to when G0-T0 was in power. With his vast knowledge of the underworld, galactic politics, and galactic history, he knows of it and what the planet holds. It would be a simple thing for him to aquire the animals of the planet, seeing as both were sold on the Black Market.
These beast are vicious canines that hunt using the Force. They would probably be empowered by the Dark Side Nexus of Malachor and would be skilled at taking down Sith, as they travel in packs and specialize in ripping people to shreds (after paralyzing them with their tails).
These amazing reptiles mitigate force usage in the area surrounding them. No more lightning, no more force-leaps, nothing. The area expands while they're in groups, so if G0-T0 were to deploy a couple of these with each of his HK units, they'd be unstoppable. These ysalamir could also stop the effects of the Drak Side Nexus, allowing G0-T0 to land non-force sensitive troops on the planet.
Oh, btw, the Gand were mostly force-sensitive. So G0-T0 would have more than just HK-50s on Malachor. Not to mention the thousands of droids on Nar Shaddaa he controls.