For a Circle of Spores druid, they are able to add 1d6 Poison Damage to their melee weapon attacks while their Symbiotic Entity feature is active.
At 2nd level, you gain the ability to channel magic into your spores. [...] While this feature is active, you gain the following benefits:
- Your melee weapon attacks deal an extra 1d6 poison damage to any target they hit.
These benefits last for 10 minutes, until you lose all these temporary hit points, or until you use your Wild Shape again.
—Circle of Spores, Guildmaster's Guide to Ravnica, pg. 27
When a [melee weapon] attack from Green-Flame Blade hits a target, the spell causes an adjacent creature to also take damage:
[...] On a hit, the target suffers the attack's normal effects, and green fire leaps from the target to a different creature of your choice that you can see within 5 feet of it. The second creature takes fire damage equal to your spellcasting ability modifier.
—Green-Flame Blade, Sword Coast Adventurer's Guide, pg. 143
For the purposes of Symbiotic Entity (or any other feature that adds damage to "any targets hit by melee weapon attacks"), does the extra damage (on the second target) associated with Green-Flame Blade count as being hit by that damage, making them eligible for the extra poison damage from Symbiotic Entity? Or does being "hit" by an effect necessarily involve an attack roll?