Can you get battle pass skins from loot box?

They are exclusive to the Battle Pass. Here are a couple relevant questions from the Season 2 Battle Pass FAQ:

What if I don’t buy the Battle Pass? Can I still earn rewards for free?

Yes. Even if you don’t purchase the Battle Pass, you can still earn the following items for free:

• The Wattson Hot Rod skin
• Five Apex Packs
• Season 2 Stat Trackers for each Legend

Will the Battle Pass rewards ever return after Season 2?

No. All Battle Charge cosmetic rewards (excluding Apex Packs and content dropped from them) in the Battle Pass are exclusive to Season 2 and will never be available again. Players in future seasons will be jealous of your OG status.