Can the monk's Stunning Strike feature be used with Martial Arts?

Question

The monk's Stunning Strike feature reads as follows:

Starting at 5th level, you can interfere with the flow of ki in an opponent’s body. When you hit another creature with a melee weapon attack, you can spend 1 ki point to attempt a stunning strike. The target must succeed on a Constitution saving throw or be stunned until the end of your next turn.

My question is, does Martial Arts count as Melee Weapons for the purpose of determining this effect? Or should the Monk be attacking with a weapon?

The confusion isn't cleared when reading the Martial Arts section, since it seems to separate Melee Weapons from Unarmed Strikes:

You can roll a d4 in place o f the normal damage of your unarmed strike or monk weapon. This die changes as you gain monk levels, as shown in the Martial Arts column of the Monk table.

So, is it possible?

Answer 1

Yes. Making an unarmed strike is a melee weapon attack regardless of whether you're looking at the original PHB printing (they're listed in the table of melee weapons) or the errata (which says unarmed strikes may be used instead of a weapon to make a melee weapon attack) and therefore satisfy Stunning Strike's requirement for a melee weapon attack.

(The second quote isn't separating unarmed strikes from melee weapons, it's separating unarmed strikes from monk weapons, which are a category of manufactured weapon.)

Answer 2

Yes, Stunning Strike can be used with Martial Arts. This was true in the original PHB and is still true when considering errata published in 2015.

Although unarmed strikes are no longer listed as melee weapons on the weapons table.

Weapons (p. 149). Unarmed strike doesn’t belong on the Weapons table.

Another change explicitly classifies an unarmed strike as a melee weapon attack in spite of not really being weapons.

Melee Attacks (p. 195). The rule on unarmed strikes should read as follows:
“Instead of using a weapon to make a melee weapon attack, you can use an unarmed strike: a punch, kick, head-butt, or similar forceful blow (none of which count as weapons). On a hit, an unarmed strike deals bludgeoning damage equal to 1 + your Strength modifier. You are proficient with your unarmed strikes.”

(NOTE: The purpose of the distinction is to prevent, for example: attempting to use an ability to enchant a weapon on a body part.)

There is more general discussion on this subject in this question.

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As an aside: it would be somewhat incongruous to simultaneously encourage unarmed combat and include features that simply don't work when unarmed. I'm not saying these sorts of inconsistencies don't happen. Rather that's the sort of highly contradictory design that would usually require very careful justification for designers to include.