The amount of investment it needs to get past Chansey is too high to be worth it in my opinion (you need like 96 EVs to 2HKO with Rocks), and it's not like Chansey is hard to take advantage of anyway. Either wear it down beforehand or have something else kill it.
Also Tyranitar just dies to Superpower or gets 2HKO'd by Flash Cannon after Rocks so you don't need investment.
0 Atk Life Orb Hydreigon Superpower vs. 0 HP / 4 Def Tyranitar: 432-510 (126.6 - 149.5%) -- guaranteed OHKO
252+ SpA Life Orb Hydreigon Flash Cannon vs. 0 HP / 0 SpD Tyranitar in Sand: 161-192 (47.2 - 56.3%) -- guaranteed 2HKO after Stealth Rock
0 Atk Life Orb Hydreigon Superpower vs. 248 HP / 252+ Def Tyranitar: 317-374 (78.6 - 92.8%) -- 37.5% chance to OHKO after Stealth Rock
Ice Beam from Support T-Tar fails to OHKO even if you're Naive if it matters.