Currently, the D&D Beyond Drops content is NOT AL-legal. This is from 3 sources:
LaTia (Community Manager) said:
Not right now; the organized play admin teams will have to deliberate on that.
https://discordapp.com/channels/516367331358801950/1501964332165107918/1501985874852712508
There was also an AMA (Ask Me Anything) on Reddit with Brian Perry (D&D Beyond’s Executive Producer) on the D&D Beyond Drops:
No, Drops content is not AL-legal.
https://www.reddit.com/r/dndbeyond/s/Oi7yeHNwLZ
Ma’at (AL Admin) said:
D&D Beyond Drops
Yesterday's general D&D announcement introduced D&D Beyond Drops, a library of maps, image reveals, stickers, character background, feats, spells, and more. And we’ve received questions on how they interact with organized play.
At the moment, they aren’t playable in AL and future AL guide updates will make this clear.
https://discordapp.com/channels/516367331358801950/1049795241433124935/1502370172479209653