Latios? Likely but not guaranteed for neutral nature.
Latias? No. As long as Latias has Soul Dew, +1 neutral nature Bug Buzz will never OHKO it (and +1 Modest only has a very low chance to OHKO after SR). To be fair though, Latias can only do HP Fire back to get any kind of response, and that is becoming less and less common. I guess Thunder could work against Genesect too if you get the parahax?
Do you realize that Genesect will always get an Attack boost against Lati@s? What are you thinking? My point still stands that a U-turn/Bug Buzz Genesect can always OHKO Mewtwo / Darkrai / Lati@s.
About Explosion.. I really don't see the need of using Explosion on a Choice Scarf set, it seems like such a waste of a moveslot IMO. A Life Orb Max Attack set seems rather gimmicky when you're taking damage from U-Turn and sacrificing Gene for an Explosion.