https://replay.pokemonshowdown.com/gen8anythinggoes-1430736966
Here's a replay.
Oh, and to confirm that did, in fact, do 1 HP of damage, here's calc.
Lvl 1 0- Atk burned Nincada Leech Life vs. 252 HP / 252+ Def Ho-Oh: 1-1 (0.2 - 0.2%) -- possibly the worst move ever
Possible damage amounts: (1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1)
(9 - 9% recovered)
Therefore, Yes, it does recover 1 HP total, which in this case, is around 9% of my guy nincada.